Question 1

In the number sequence 200, 200, 100, 300, 75, ?, identify the next term that should replace the question mark so that the underlying pattern is correctly maintained.

Accepted Answer

Introduction / Context: This question presents a short numerical sequence with one missing term. The numbers appear to rise and fall, which often suggests alternating operations such as multiplying and dividing by different factors. Recognizing such alternating patterns is a common requirement in competitive examinations that test numerical and logical reasoning. Given Data / Assumptions: The known sequence is: 200, 200, 100, 300, 75, ? There is a single missing term at the end, to be filled with one of the given options. We assume a single consistent pattern governs the entire sequence. Operations may alternate between multiplication and division, or between different constant factors. Concept / Approach: The first observation is that the values 200, 200, 100, 300, 75 fluctuate in a way that suggests ratios rather than simple differences. Comparing each term with the one immediately before it can reveal a pattern in terms of multipliers or divisors. If we discover a sequence of factors such as ×1, ÷2, ×3, ÷4, then we can naturally extend it to the next term by continuing that factor pattern (for example ×5). Step-by-Step Solution: Step 1: Compare each term with the previous one. 200 → 200: factor 200 / 200 = 1 (multiply by 1). 200 → 100: factor 100 / 200 = 1/2 (divide by 2). 100 → 300: factor 300 / 100 = 3 (multiply by 3). 300 → 75: factor 75 / 300 = 1/4 (divide by 4). Step 2: Recognize the pattern of factors: ×1, ÷2, ×3, ÷4. Step 3: This strongly suggests the next operation should be ×5 (continuing with 1, 2, 3, 4, 5 as multipliers or divisors). Step 4: Apply the factor ×5 to the last known term: 75 × 5 = 375. Step 5: Therefore the missing term is 375. Verification / Alternative check: We can list the pattern of operations explicitly: 200 × 1 = 200, 200 ÷ 2 = 100, 100 × 3 = 300, 300 ÷ 4 = 75, and now 75 × 5 = 375. The multipliers and divisors 1, 2, 3, 4, 5 are in natural ascending order, split alternately between multiplication and division. There is no inconsistency in this explanation, making the pattern clear and robust. Why Other Options Are Wrong: Options such as 150, 175 or 250 do not fit the systematic factor pattern. For instance, 75 × 2 = 150, but that would correspond to ×2, which breaks the smooth continuation after ÷4. Similarly, 175 and 250 require arbitrary factors that do not extend the observed sequence 1, 2, 3, 4. Thus they fail to maintain a simple, consistent rule across all terms. Common Pitfalls: A frequent mistake is to examine only the differences between consecutive terms (0, -100, +200, -225, …), which appear irregular and difficult to generalize. Another pitfall is to stop after testing only one or two possible rules instead of verifying the pattern across the entire sequence. Always ensure that any proposed rule works for every transition, not just part of the series. Final Answer: Continuing the alternating pattern of ×1, ÷2, ×3, ÷4 with ×5, the missing term must be 375.

Question 2

Consider the series 2, 16, 3, 81, 4, ?. Each pair of numbers appears to follow a mathematical rule. What number should replace the question mark so that the pattern is preserved?

Accepted Answer

Introduction / Context: This question presents a short alternating series that consists of a small number followed by a larger one, repeated. Problems of this type are usually based on exponentiation, squares, cubes or simple functional relationships between each small number and the large number that follows it. The goal is to identify that relationship and then apply the same idea to the final pair involving the number 4 and the missing term. Given Data / Assumptions: The series is: 2, 16, 3, 81, 4, ? Numbers appear in pairs: (2, 16), (3, 81), (4, ?). We assume the same rule applies to each pair. The rule is likely to involve powers of the first number in each pair. Concept / Approach: When we see a small integer followed by a much larger one, powers are a natural candidate: n^2, n^3, n^4 etc. Checking 2 and 16, and 3 and 81 quickly suggests that these are perfect fourth powers, since 2^4 = 16 and 3^4 = 81. If this pattern holds, then the next term should be 4 raised to the same power. This approach is straightforward and matches common exam patterns. Step-by-Step Solution: Step 1: Examine the first pair (2, 16). Compute 2^2 = 4, 2^3 = 8 and 2^4 = 16. The second element 16 equals 2^4. Step 2: Examine the second pair (3, 81). Compute 3^2 = 9, 3^3 = 27 and 3^4 = 81. The second element 81 equals 3^4. Step 3: Recognize the pattern: each larger term is the fourth power of the smaller term that precedes it. Step 4: Apply this pattern to the final pair (4, ?). Compute 4^4 = 4 * 4 * 4 * 4 = 16 * 16 = 256. Step 5: Therefore, the missing term must be 256. Verification / Alternative check: We can confirm that no other simple exponent pattern fits as neatly. If we tried squares, 2^2 = 4 and 3^2 = 9 would not match 16 and 81. Cubes 2^3 = 8, 3^3 = 27 also fail. The fourth power pattern exactly explains both known pairs, making it the most natural and reliable rule. Applying it to 4 gives a clean integer result, 256, strengthening our confidence. Why Other Options Are Wrong: Values like 99, 125 or 396 do not equal 4^k for any small integer k. In particular, 125 is 5^3, which would require the base in the pair to be 5, not 4. Similarly, 396 has no direct simple power relationship with 4. Because the existing pairs both follow a perfect fourth power pattern, any choice that does not equal 4^4 breaks the consistency of the sequence. Common Pitfalls: Some learners may look for differences or ratios across the entire line of numbers (for example, from 2 to 16 to 3 to 81) instead of respecting the natural pairing structure. Others may guess square or cube patterns without checking both given pairs. It is important to verify that the rule works for all existing examples before applying it to the missing term. Final Answer: Following the pattern that each second number is the fourth power of the first, the missing term corresponding to 4 is 256.

Question 3

In the series 1, 2, 6, 15, 31, 56, x, choose the correct value of x so that the sequence continues to follow a consistent pattern.

Accepted Answer

Introduction / Context: This is a classic increasing number series where each term is larger than the previous one by a growing amount. Such sequences often rely on patterns in the differences between consecutive terms, and those differences may themselves form squares, cubes or an arithmetic progression. The goal is to identify the structure and then use it to calculate the missing value x. Given Data / Assumptions: The given series is: 1, 2, 6, 15, 31, 56, x. Only one term (x) is missing at the end. We assume a single simple rule, or a small set of related rules, generates all terms. Differences between consecutive terms are likely to hold the key. Concept / Approach: The simplest approach is to compute the first level differences between consecutive terms. If these differences follow a recognizable pattern (for example, they are perfect squares or form their own arithmetic series), we can extend that pattern to find the next difference. Adding that next difference to the last known term gives us x. This two layer structure is very common in reasoning tests: a series whose differences are themselves patterned. Step-by-Step Solution: Step 1: Compute the differences between consecutive terms. 2 - 1 = 1. 6 - 2 = 4. 15 - 6 = 9. 31 - 15 = 16. 56 - 31 = 25. Step 2: List the differences: 1, 4, 9, 16, 25. Step 3: Recognize that these are perfect squares: 1^2, 2^2, 3^2, 4^2, 5^2. Step 4: The next difference in this pattern should be 6^2 = 36. Step 5: Add this next difference to the last known term: 56 + 36 = 92. Step 6: Hence, x = 92. Verification / Alternative check: We can reconstruct the series from the beginning using the rule: start at 1, then keep adding consecutive squares: 1 + 1 = 2, 2 + 4 = 6, 6 + 9 = 15, 15 + 16 = 31, 31 + 25 = 56, and finally 56 + 36 = 92. Each step is consistent, and the pattern of squared differences is smooth and unbroken. This is strong evidence that the identified rule is correct. Why Other Options Are Wrong: Values like 65, 78 or 81 would require the next difference to be 9, 22 or 25 rather than 36, disrupting the pattern of perfect squares. Those values can only be obtained by using ad hoc differences rather than extending the simple 1^2, 2^2, 3^2, 4^2, 5^2, 6^2 pattern. Since such irregular changes are not supported by the earlier part of the series, these options are inconsistent and therefore incorrect. Common Pitfalls: Learners sometimes try to fit a direct formula to the nth term, which can be tedious and unnecessary here. Another mistake is to notice that the series appears irregular at first sight and stop exploring after checking only one or two differences. By carefully examining all differences and recognizing them as consecutive squares, the structure becomes simple and elegant. Final Answer: Continuing the pattern of adding consecutive squares to each term, the missing value x is 92.

Question 4

In the series 169, 144, 121, 100, 85, 64, one term does not fit the underlying pattern. Identify the wrong term in this sequence.

Accepted Answer

Introduction / Context: Here we are given a descending series of numbers and asked to find the term that breaks the pattern. Many such sequences are built from squares, cubes or other well known number sets. Recognizing a standard structure such as consecutive perfect squares makes it much easier to detect the intruder that does not belong. Given Data / Assumptions: The series is: 169, 144, 121, 100, 85, 64. Exactly one term is incorrect with respect to a simple underlying rule. The other terms are assumed to follow a clean, mathematical pattern. The list is in strictly descending order apart from the anomaly. Concept / Approach: The numbers 169, 144, 121, 100 and 64 are all familiar because many of them are common perfect squares: 13^2, 12^2, 11^2, 10^2 and 8^2 respectively. This strongly suggests that the true series should be a descending run of square numbers. If so, the term between 100 and 64 should also be a perfect square. By comparing what we expect with the given 85, we can quickly identify the incorrect number. Step-by-Step Solution: Step 1: Express each known term as a square if possible. 169 = 13^2. 144 = 12^2. 121 = 11^2. 100 = 10^2. 64 = 8^2. Step 2: Note that these squares involve decreasing bases: 13, 12, 11, 10, (9), 8. Step 3: The missing square in this descending sequence should be 9^2 = 81, which should appear between 10^2 = 100 and 8^2 = 64. Step 4: The given term in that position is 85, which is not a perfect square and does not equal 81. Step 5: Therefore 85 is the inconsistent term and is the wrong number in the series. Verification / Alternative check: If we rewrite the corrected sequence as 169 (13^2), 144 (12^2), 121 (11^2), 100 (10^2), 81 (9^2), 64 (8^2), we clearly see a smooth pattern: the base of each square decreases by 1 at each step. The appearance of 85 breaks this otherwise perfect run of consecutive squares, confirming it as the outlier. Why Other Options Are Wrong: Each of the other candidates is a genuine perfect square: 169, 144, 121, 100, and 64 correspond to 13^2, 12^2, 11^2, 10^2 and 8^2. Removing any of these would destroy the clear and elegant structure of descending squares. Only 85 is not a square, so it is the only term that disrupts the pattern. Common Pitfalls: Sometimes students look at the differences between terms (for example 169 – 144 = 25, 144 – 121 = 23, etc.) and attempt to find patterns there, which are more complicated and less revealing. Instead, recognizing the base numbers that square to these values is faster and more reliable. Another pitfall is to assume that every series must have a constant difference, which is not true for square sequences. Final Answer: The only term that does not fit the descending sequence of perfect squares is 85.

Question 5

In the alphanumeric series 3F, 6G, 11I, 18L, ?, each term combines a number and a letter. Which of the following options correctly completes the pattern?

Accepted Answer

Introduction / Context: This problem involves an alphanumeric sequence where each term consists of a number followed by a letter. To solve it, we must identify independent patterns in the number part and the letter part. Such questions test the ability to handle simultaneous logical rules and to keep numerical and alphabetical progressions in mind at the same time. Given Data / Assumptions: The series is: 3F, 6G, 11I, 18L, ? Each term has a numeric component and a single uppercase letter. Exactly one term is missing at the end and must be chosen from the options. The numeric sequence and the letter sequence both follow consistent rules. Concept / Approach: We treat the numbers and letters separately. For numbers, computing differences often reveals the pattern. For letters, we convert them to alphabetical positions (A = 1, B = 2, …, Z = 26) and look at how these positions progress. Often, the number rule and the letter rule are independent but parallel, using similar ideas like increasing differences or step sizes. Once both patterns are understood, we combine them to form the missing term. Step-by-Step Solution: Step 1: Analyse the numeric part: 3, 6, 11, 18. Differences: 6 - 3 = 3, 11 - 6 = 5, 18 - 11 = 7. Step 2: Observe that the differences form the series 3, 5, 7, which are consecutive odd numbers. Step 3: The next difference should be the next odd number, 9. Step 4: So the next number is 18 + 9 = 27. Step 5: Now analyse the letter part: F, G, I, L. Convert to positions: F = 6, G = 7, I = 9, L = 12. Step 6: Differences between these positions: 7 - 6 = 1, 9 - 7 = 2, 12 - 9 = 3. Step 7: The differences are 1, 2, 3 so the next increment should be 4. Step 8: Thus the next letter position is 12 + 4 = 16, which corresponds to P. Step 9: Combining the numeric and letter patterns, the missing term is 27P. Verification / Alternative check: We can reconstruct each term using these rules. Starting from 3F, add 3 to get 6 and move from F(6) by +1 step to G(7). Then add 5 to get 11 and move +2 letters to I(9). Then add 7 to get 18 and move +3 letters to L(12). The next step is naturally +9 in numbers and +4 in letters, yielding 27P. The structure is fully consistent and symmetrical, which strongly confirms the solution. Why Other Options Are Wrong: Terms like 27Q, 25N or 21O break at least one of the patterns. For example, 25N would require the numeric sequence to skip from 18 to 25 (difference 7 instead of 9) and the letter sequence to jump to N(14), which does not follow the +4 increment from L(12). Likewise, 27Q uses the correct number 27 but the letter Q(17) is one step ahead of the correct position 16 (P). Common Pitfalls: A frequent error is to treat the pair as a single unit and look for very complex transformations, rather than splitting the analysis into numeric and alphabetic parts. Another pitfall is to spot only the number pattern and then guess a random letter, which might coincidentally look plausible but will not survive a careful position based check. Final Answer: The correct term that continues both the number pattern of increasing odd differences and the letter pattern of increasing step sizes is 27P.

Question 6

In the alphanumeric series Q1F, S2E, U6D, W21C, ?, identify the next term that correctly follows the combined pattern of letters and numbers.

Accepted Answer

Introduction / Context: This problem features a more elaborate alphanumeric series in which both the letters and the numbers follow nontrivial patterns. The task is to decode these separate structures and then combine them to find the missing term. Such questions test pattern recognition with both arithmetic reasoning and alphabet position logic. Given Data / Assumptions: Given terms: Q1F, S2E, U6D, W21C, ? Each term has the format: letter, number, letter. We assume the first letters, the middle numbers, and the last letters each obey a consistent pattern. The missing term must follow all these patterns simultaneously. Concept / Approach: The safest method is to isolate each component sequence: the sequence of first letters, the sequence of middle numbers, and the sequence of last letters. For letters, we map them to their alphabet positions. For numbers, we look for arithmetic or multiplicative relationships. The middle numbers here grow quickly (1, 2, 6, 21), which hints at a multiplicative rule rather than simple addition. Step-by-Step Solution: Step 1: Analyse the first letters: Q, S, U, W. Positions: Q = 17, S = 19, U = 21, W = 23. Step 2: Differences: 19 - 17 = 2, 21 - 19 = 2, 23 - 21 = 2. So the first letters increase by 2 positions each time. Step 3: Next first letter position: 23 + 2 = 25, which is Y. Step 4: Analyse the last letters: F, E, D, C. Positions: F = 6, E = 5, D = 4, C = 3. Step 5: These decrease by 1 each time: 6 → 5 → 4 → 3, so the next last letter is position 2, which is B. Step 6: Now examine the middle numbers: 1, 2, 6, 21. Step 7: Look for a multiplicative pattern. Check 1 → 2: 1*1 + 1 = 2. Check 2 → 6: 2*2 + 2 = 6. Check 6 → 21: 6*3 + 3 = 21. Step 8: We see a pattern n → n*k + k, with k increasing by 1: k = 1, 2, 3. Step 9: The next step uses k = 4: 21*4 + 4 = 84 + 4 = 88. Step 10: Therefore the next term is Y88B. Verification / Alternative check: We can recompute the sequence from the start using the identified rules. First letters: 17, 19, 21, 23, 25 → Q, S, U, W, Y. Last letters: 6, 5, 4, 3, 2 → F, E, D, C, B. Middle numbers: start at 1 and repeatedly apply n → n*k + k with k = 1, 2, 3, 4. This gives 1, 2, 6, 21, 88. These recomputed values match all the known terms and yield Y88B as the next, verifying the pattern. Why Other Options Are Wrong: Z88B has the correct middle number and last letter but the wrong first letter, because Z is position 26, not 25. Y44B has correct letters but an incorrect middle number that does not satisfy the n*k + k pattern. K25P breaks both the letter and number patterns. Thus only Y88B is consistent with all three components of the sequence. Common Pitfalls: A common error is to focus solely on the letters (which form relatively simple progressions) and then guess the middle number. Another trap is to assume that the numbers grow by fixed increments, which fails immediately after 1 and 2. Careful stepwise analysis of each component prevents such mistakes and reveals the deeper multiplicative pattern in the middle numbers. Final Answer: The term that satisfies the pattern in the first letters, middle numbers and last letters is Y88B.

Question 7

In the mixed numeric–alphabetic pattern 1A2, 3C4, 7G8, ___, which of the following terms should come next to correctly extend the sequence?

Accepted Answer

Introduction / Context: This question involves a hybrid series in which each term consists of a number, a letter and another number. Solving such problems requires simultaneously tracking how the numbers change from term to term and how the letters progress through the alphabet. The pattern here links the growth of the outer numbers and the shifts in the central letter in a systematic way. Given Data / Assumptions: Known terms: 1A2, 3C4, 7G8, ___. Each term has the structure: number, letter, number. Exactly one term is missing, and must be chosen from the options. We assume that both the numeric parts and the letter part follow consistent rules. Concept / Approach: We split the problem into three related sequences: the first numbers (1, 3, 7, ?), the middle letters (A, C, G, ?), and the last numbers (2, 4, 8, ?). We then look for patterns in each. The numbers may grow by changing differences or by doubling; the letters may advance by skipping a fixed number of positions or by using the same step pattern as the outer numbers. Once these three subpatterns are identified, they must all point to the same candidate term. Step-by-Step Solution: Step 1: Analyse the first numbers: 1, 3, 7. Differences: 3 - 1 = 2, 7 - 3 = 4. Step 2: The increments themselves (2, 4) appear to double, suggesting the next increment should be 8. Step 3: So the next first number is 7 + 8 = 15. Step 4: Analyse the last numbers: 2, 4, 8. This is a simple doubling sequence: 2, 4, 8, so the next term is 8 * 2 = 16. Step 5: Now look at the middle letters: A, C, G. Positions: A = 1, C = 3, G = 7. Step 6: Differences: 3 - 1 = 2, 7 - 3 = 4, mirroring the first number differences. Step 7: The next increment should again be 8, so the next letter position is 7 + 8 = 15, which is O. Step 8: Combining these results, the missing term is 15O16. Verification / Alternative check: We can represent the pattern more compactly as a triple progression: the outer numbers follow 1, 3, 7, 15 (each time adding 2, 4, 8), while the inner letters correspond to positions 1, 3, 7, 15, and the final numbers are 2, 4, 8, 16 (successive doublings). All three components are driven by the same doubling rule for the increments, which gives a strong and elegant structural explanation. Why Other Options Are Wrong: 16P17 does not match any of the three subpatterns: 16 is not the correct next first number, P(16) is one step beyond the correct letter O(15), and 17 is not a doubling of 8. Similarly, 14O15 and 13P14 either use partial aspects of the discovered pattern or none at all, but they fail to align all three parts simultaneously. Only 15O16 is consistent with every progression in the series. Common Pitfalls: Some students may focus on only one side of the term, such as the last numbers, and then guess the remaining parts. Others may overlook the fact that the differences between letter positions mirror the differences between the first numbers. Ignoring this connection can lead to plausible but incorrect guesses. Always cross check each component of the candidate term with all identified rules. Final Answer: The only option that continues the numerical and alphabetic patterns correctly is 15O16.

Question 8

In the series 64, 2, 32, 72, 3, 24, 76, 4, 19, ?, 5, 15.6, each group of three numbers follows a consistent rule. Which number should replace the question mark to preserve the pattern?

Accepted Answer

Introduction / Context: This sequence alternates between larger and smaller numbers and includes a decimal entry at the end, which suggests that the series may be organised in blocks rather than as a simple one dimensional progression. Grouping the terms into triplets and checking relationships within each group is a powerful approach for this sort of question. Given Data / Assumptions: The full sequence is: 64, 2, 32, 72, 3, 24, 76, 4, 19, ?, 5, 15.6. There is a single missing value between 19 and 5. Examining the numbers suggests grouping in triplets: (64, 2, 32), (72, 3, 24), (76, 4, 19), (?, 5, 15.6). We assume each triplet follows a similar numeric rule. Concept / Approach: Within each group of three, the middle number often acts as an operator or divisor linking the first and third numbers. A very natural idea is to test whether the first number divided by the second equals the third number. If this holds for several triplets, we can assume the same relation should hold for the triplet that contains the missing term and solve for that unknown value using simple algebraic rearrangement. Step-by-Step Solution: Step 1: Look at the first triplet: 64, 2, 32. Check the relation 64 ÷ 2 = 32, which is true. Step 2: Look at the second triplet: 72, 3, 24. Check 72 ÷ 3 = 24, which is also true. Step 3: Look at the third triplet: 76, 4, 19. Check 76 ÷ 4 = 19, again true. Step 4: Conclude that in each triplet, first number ÷ second number = third number. Step 5: Apply this rule to the last triplet (?, 5, 15.6). We must have ? ÷ 5 = 15.6. Step 6: Multiply both sides by 5 to solve for the missing term: ? = 15.6 * 5. Step 7: Compute 15.6 * 5 = 78.0, so the missing number is 78. Verification / Alternative check: We can verify numerically by reconstructing the entire set of triplets with the proposed value. The four groups become (64, 2, 32), (72, 3, 24), (76, 4, 19), and (78, 5, 15.6). Each satisfies the rule first ÷ second = third. Furthermore, the first terms within the groups form a mild progression (64, 72, 76, 78), and the middle terms rise by 1 each time (2, 3, 4, 5), which is a natural secondary structure supporting our conclusion. Why Other Options Are Wrong: If we tested 80, 72 or 70, then first ÷ second would not equal 15.6. For example, 80 ÷ 5 = 16, not 15.6; 72 ÷ 5 = 14.4; 70 ÷ 5 = 14. None of these match the third element of the last triplet. Therefore, they break the consistent rule that held in the previous groups. Common Pitfalls: A common mistake is to treat the entire sequence as a single chain and look for one step differences or ratios between every pair of successive numbers. The presence of the repeating small numbers 2, 3, 4, 5 hints that the series should instead be broken into segments. Ignoring this structure makes the pattern appear much more complex than it really is. Final Answer: To maintain the relation first ÷ second = third within each triplet, the missing term must be 78.

Question 9

From the series 7, 18, 40, 106, 183, 282, 403, one term is inconsistent with the underlying numeric pattern. Which number is the wrong term?

Accepted Answer

Introduction / Context: This question asks us to identify an incorrect term in an increasing number sequence. The numbers grow rapidly, which suggests that the pattern is in the differences or in a second level series rather than a simple linear progression. Detecting such higher order patterns is a key skill in advanced number series problems. Given Data / Assumptions: The series given is: 7, 18, 40, 106, 183, 282, 403. Exactly one term is wrong and must be identified. We assume that the underlying correct sequence follows a reasonably simple rule, likely in the differences between terms. The differences themselves may have a recognizable pattern, for example multiples of a constant. Concept / Approach: To find the wrong term, we compare consecutive differences first. If these differences do not immediately show a clear structure, we examine whether they are all multiples of some number or follow a simple pattern with one anomaly. In this sequence, the differences turn out to be multiples of 11, hinting at a deeper pattern in which one of the increments is inconsistent with the rest and therefore points to the incorrect term. Step-by-Step Solution: Step 1: Compute differences between consecutive terms. 18 - 7 = 11. 40 - 18 = 22. 106 - 40 = 66. 183 - 106 = 77. 282 - 183 = 99. 403 - 282 = 121. Step 2: Note that these differences are 11, 22, 66, 77, 99, 121. Step 3: Factor each difference by 11: 11*(1, 2, 6, 7, 9, 11). Step 4: Suspect a simpler intended pattern such as using consecutive odd multiples of 11: 11, 33, 55, 77, 99, 121 (i.e., 11*1, 11*3, 11*5, 11*7, 11*9, 11*11). Step 5: Reconstruct the series using these intended differences, starting from 7. Next term: 7 + 11 = 18 (matches). Next term: 18 + 33 = 51 (should be here). Next term: 51 + 55 = 106 (matches 106). Then: 106 + 77 = 183; 183 + 99 = 282; 282 + 121 = 403, all matching the given sequence. Step 6: The only mismatch is at the position where 51 should appear; the given term is 40. Step 7: Therefore, 40 is the wrong term in the series. Verification / Alternative check: The corrected series is 7, 18, 51, 106, 183, 282, 403. Its differences are 11, 33, 55, 77, 99, 121, exactly 11 times the odd numbers 1, 3, 5, 7, 9, 11. This pattern is elegant, symmetric and fully consistent. The fact that only one given term (40) disrupts this otherwise perfect progression confirms it as the erroneous entry. Why Other Options Are Wrong: Removing 18, 106, 183 or 282 would destroy the smooth sequence of differences that are all odd multiples of 11. With those terms in place, the increments remain neatly patterned once we correct the third term to 51. Therefore, none of the other options can be considered the unique wrong term. Common Pitfalls: It is easy to be misled by the large jumps (for example 40 to 106 and 106 to 183) and give up on finding a simple pattern. Some students may also attempt to fit a complex formula for the nth term instead of exploiting the structure in the differences. The key insight here is to notice that all differences are near multiples of 11 and then refine the idea to odd multiples of 11, which exposes the single anomaly cleanly. Final Answer: The term that breaks the intended pattern of odd multiples of 11 as differences is 40.

Question 10

In the series 6, 12, 21, x, 48, identify the value of x that continues the same number pattern between the terms.

Accepted Answer

Introduction / Context: This is a moderately simple increasing series with one missing term. The jumps between numbers grow in a regular way, which suggests that the differences between consecutive terms form their own arithmetic pattern. Determining these differences and extending the pattern enables us to find x. Given Data / Assumptions: The known terms are 6, 12, 21, x, 48. Only one term, x, is missing. A single, consistent rule is assumed to generate the progression. Differences between successive terms are the natural first place to look for structure. Concept / Approach: We compute and inspect the first level differences. If these differences themselves follow an arithmetic pattern (for example, they increase by a constant amount), then we can extend that difference pattern to find the missing value and thus recover x. This kind of two stage progression is very common in number series questions. Step-by-Step Solution: Step 1: Compute known differences between consecutive terms. 12 - 6 = 6. 21 - 12 = 9. Step 2: Let x be the next term and 48 be the last term. Then the remaining differences are x - 21 and 48 - x. Step 3: Look at the existing differences: 6 and 9. The increase from 6 to 9 is +3, so it is reasonable to expect the next differences to be 12 and 15, continuing this pattern: 6, 9, 12, 15. Step 4: Set x - 21 = 12, because this should be the third difference. Solving, x = 21 + 12 = 33. Step 5: Check the last difference: 48 - x = 48 - 33 = 15, which matches the expected fourth difference. Step 6: Therefore x = 33 fits perfectly. Verification / Alternative check: Write out the completed series with x = 33: 6, 12, 21, 33, 48. Now list the differences: 12 - 6 = 6, 21 - 12 = 9, 33 - 21 = 12, 48 - 33 = 15. The differences are 6, 9, 12, 15, an arithmetic sequence with common difference 3. This neat structure confirms that we have identified the correct missing term. Why Other Options Are Wrong: If x were 30, the differences would be 6, 9, 9, 18, which break the +3 pattern. If x were 42, the last difference 48 - 42 would be 6 instead of 15. Similarly, x = 45 or any other value not equal to 33 fails to create a smooth arithmetic progression of differences. Thus these alternatives do not maintain the simple rule that governs the series. Common Pitfalls: One common pitfall is to try only a couple of options and test them numerically, rather than systematically deriving the pattern in the differences. Another is to assume that the differences should be constant, which does not fit here. Recognizing an arithmetic series in the first level differences is the key to an efficient and reliable solution. Final Answer: The value of x that continues the pattern of increasing differences (6, 9, 12, 15) is 33.

Question 11

In the alphanumeric series P3C, R5F, T8I, V12L, ?, determine the next term that correctly extends both the numeric and alphabetic patterns.

Accepted Answer

Introduction / Context: This is an alphanumeric series where each term consists of a letter, a number, and another letter. The sequence P3C, R5F, T8I, V12L, ? encodes simultaneous patterns in the first letters, the middle numbers, and the last letters. Uncovering these patterns and applying them in a coordinated way allows us to determine the missing term. Given Data / Assumptions: Given terms: P3C, R5F, T8I, V12L, ? Each term has the format: letter, number, letter. The first and last letters are uppercase English letters. The middle numbers increase from term to term in a non constant way. Concept / Approach: We split the analysis into three parts: the first letters, the middle numbers, and the last letters. For letters, we convert them into positions in the alphabet. For the numbers, we calculate differences to see whether they follow their own pattern. Often, the changes in letters and numbers mirror each other or follow related progressions, which helps confirm the correct rule. Step-by-Step Solution: Step 1: Analyse the first letters: P, R, T, V. Positions: P = 16, R = 18, T = 20, V = 22. Step 2: The positions increase by 2 each time: 16 → 18 → 20 → 22. Step 3: So the next first letter should be at position 24, which is X. Step 4: Analyse the last letters: C, F, I, L. Positions: C = 3, F = 6, I = 9, L = 12. Step 5: These positions increase by 3 each time: 3 → 6 → 9 → 12. Step 6: The next last letter should be at position 15, which is O. Step 7: Analyse the middle numbers: 3, 5, 8, 12. Step 8: Compute differences: 5 - 3 = 2, 8 - 5 = 3, 12 - 8 = 4. The increments are 2, 3, 4. Step 9: The next increment should be 5, giving the next middle number as 12 + 5 = 17. Step 10: Combining these results, the missing term is X17O. Verification / Alternative check: We can reconstruct the entire pattern using the identified rules. First letters: P(16), R(18), T(20), V(22), X(24), a sequence with constant increment +2. Last letters: C(3), F(6), I(9), L(12), O(15), a sequence with constant increment +3. Middle numbers: start from 3 and add 2, 3, 4, 5 to get 3, 5, 8, 12, 17. This yields the exact given series plus X17O as the next term, confirming the logic. Why Other Options Are Wrong: X17M has the correct first letter and number but wrong final letter; M is position 13, not 15. X16O uses correct letters but a number that ignores the +2, +3, +4, +5 increment pattern. Y17O has correct middle and last parts but the first letter Y(25) breaks the +2 step from V(22). Therefore only X17O satisfies all three aligned patterns. Common Pitfalls: A common error is to spot the letter pattern but not verify the numeric pattern, or vice versa. Another mistake is to assume that the letters are random and focus only on the numbers. However, in such alphanumeric series both sequences are almost always meaningful. Carefully checking each component against the candidate answer avoids these partial or accidental matches. Final Answer: The correct term that continues the pattern in both letters and numbers is X17O.

Question 12

Using the arrangement H T 6 # E 7 $ K I L % 3 P @ 2 A J R U 4 * V D, the series T#6 7K$ L3% ? is formed by following a fixed pattern. What should replace the question mark in this series?

Accepted Answer

Introduction / Context: This question is based on a fixed arrangement of letters, digits and symbols placed in a single linear sequence. The series T#6 7K$ L3% ? is derived from that arrangement by selecting and reordering groups of three consecutive characters in a consistent way. The task is to identify the underlying rule and predict what the next triple should look like. Given Data / Assumptions: The base arrangement is: H T 6 # E 7 $ K I L % 3 P @ 2 A J R U 4 * V D. We index the positions from left to right starting at 1. The derived series is: T#6, 7K$, L3%, ? Each term in the series consists of exactly three characters. The same selection and reordering pattern is applied for each term. Concept / Approach: First, we locate each given triple inside the base arrangement and see which three adjacent characters they come from. Then we observe how the positions of those characters are rearranged to form the triple. If the starting positions of these source triplets follow a simple progression (for example +4 each time), we can find the starting position of the next source triplet and apply the same reordering rule to derive the missing triple. Step-by-Step Solution: Step 1: Write down the indexed base arrangement. 1:H, 2:T, 3:6, 4:#, 5:E, 6:7, 7:$, 8:K, 9:I, 10:L, 11:%, 12:3, 13:P, 14:@, 15:2, 16:A, 17:J, 18:R, 19:U, 20:4, 21:*, 22:V, 23:D. Step 2: Identify the source characters for "T#6". Positions 2, 3, 4 hold T, 6, #, i.e., the triple (T, 6, #). The given term is "T#6", which reorders these as (1st, 3rd, 2nd) = (T, #, 6). Step 3: Find the source for "7K$". We observe that T is at 2, 7 is at 6, $ is at 7 and K is at 8. The consecutive triple (7, $, K) is at positions 6, 7, 8. Reordering (7, $, K) as (1st, 3rd, 2nd) gives 7K$, which matches the series term. Step 4: Find the source for "L3%". The consecutive triple (L, %, 3) occurs at positions 10, 11, 12. Reordering (L, %, 3) as (1st, 3rd, 2nd) gives L3%, matching the given term. Step 5: Notice that the starting indices of these source triples are 2, 6 and 10, which increase by 4 each time. Step 6: The next source triple should therefore start at position 14: characters at 14, 15, 16 are (@, 2, A). Step 7: Apply the same reordering (1st, 3rd, 2nd) to (@, 2, A) to get @A2. Verification / Alternative check: We can summarise the rule as: take every fourth triple starting from positions 2, 6, 10, 14, and within each triple (x, y, z) output x, z, y. This rule perfectly explains T#6 (from T, 6, #), 7K$ (from 7, $, K) and L3% (from L, %, 3). Applying it consistently to (@, 2, A) gives @A2. Since this specific combination is not present among the options, the only valid choice is that none of the given options match the correct triple. Why Other Options Are Wrong: The options @2A, A@2 and 2A@ are all different permutations of (@, 2, A), but none follow the established (1st, 3rd, 2nd) reordering pattern. Therefore, although they use the right characters, their order is inconsistent with the rule. The only truthful statement among the choices, given the correct triple @A2, is that none of the given options is correct. Common Pitfalls: Students may confuse the base order of characters with the derived order and may attempt to guess the next triple without carefully tracking indices. Another pitfall is to assume that any permutation containing the correct three symbols must be valid. However, in such questions, the exact order usually encodes the pattern, so ignoring it leads to incorrect conclusions. Final Answer: The pattern yields the triple @A2, which is not among the listed options, so the correct choice is None of these.

Question 13

In the number series 118, 166, 190, 202, 208, ?, identify the next term that correctly follows the observed pattern.

Accepted Answer

Introduction / Context: This problem presents a moderately increasing sequence and asks for the next term. The increments between numbers shrink in a regular manner, hinting that the differences between consecutive terms themselves follow a simple rule. Recognising this second level progression is key to solving the question efficiently. Given Data / Assumptions: The series is: 118, 166, 190, 202, 208, ? There is exactly one missing term at the end. We assume a single, consistent pattern governs the differences. No term is intended as an outlier or exception. Concept / Approach: The most natural step is to compute the first level differences between consecutive terms and see whether these differences themselves form a simple sequence. Sometimes they may be halved, doubled, or follow an arithmetic progression. Here, the differences appear to be reducing by a factor of 2 each time, suggesting a geometric or halving pattern that can be extended one more step to find the next increment. Step-by-Step Solution: Step 1: Compute the differences between consecutive terms. 166 - 118 = 48. 190 - 166 = 24. 202 - 190 = 12. 208 - 202 = 6. Step 2: Observe that each difference is half of the previous one: 48 ÷ 2 = 24, 24 ÷ 2 = 12, 12 ÷ 2 = 6. Step 3: Continue this halving pattern. The next difference should be 6 ÷ 2 = 3. Step 4: Add this difference to the last known term to find the next term: 208 + 3 = 211. Step 5: Thus the missing term is 211. Verification / Alternative check: We can reconstruct the series using the rule "add a difference that is half of the previous one." Starting from 118, we add 48 to get 166, add 24 to get 190, add 12 to get 202, add 6 to get 208, and finally add 3 to get 211. Every step follows the same consistent halving pattern, making this a robust explanation of the series. Why Other Options Are Wrong: If we selected 222, 233 or 244, the corresponding differences from 208 would be 14, 25 or 36, none of which is half of 6. These numbers introduce a break in the clear halving sequence of increments and therefore cannot be correct. Only 211 preserves the smooth geometric pattern of the differences. Common Pitfalls: One pitfall is to attempt to fit a direct polynomial or complex formula for the nth term, which is unnecessary. Another is to assume differences must always be constant, which is not true here. Some learners also stop after noticing the first couple of differences and miss the halving pattern because they do not compute the full set. Carefully listing and examining all differences is essential. Final Answer: Following the pattern of halving differences (48, 24, 12, 6, 3), the next term in the series is 211.

Question 14

In the mixed series 11M13, 13Q17, ?, 17V22, 19W23, one alphanumeric term is missing. Which option correctly completes the sequence?

Accepted Answer

Introduction / Context: This question involves a structured series where each term combines two numbers and one letter: for example, 11M13. We must identify a consistent rule that connects the numbers and letters, and then use that rule to find the missing middle term between 13Q17 and 17V22. This requires careful attention to both the numeric and alphabetic progressions. Given Data / Assumptions: Known terms: 11M13, 13Q17, ?, 17V22, 19W23. Each term has the format: number, letter, number. We assume the numeric and letter components follow simple, consistent patterns. The missing term must align with both the number and letter rules simultaneously. Concept / Approach: We consider two number sequences: the left numbers (11, 13, ?, 17, 19) and the right numbers (13, 17, ?, 22, 23). We also examine the letters M, Q, ?, V, W and relate them to these numbers via their alphabet positions. If we can express the letters in a simple way based on the numbers (for example equal to one of the numbers), this often reveals the intended rule with minimal ambiguity. Step-by-Step Solution: Step 1: Analyse the left number sequence: 11, 13, ?, 17, 19. The pattern here is clearly +2 each time: 11 → 13 → 15 → 17 → 19. So the left number in the missing term must be 15. Step 2: Analyse the right number sequence: 13, 17, ?, 22, 23. Compute the differences: 17 - 13 = 4, ? - 17 = ?, 22 - ? = ?, 23 - 22 = 1. Notice that 13, 17, 21, 22, 23 would give differences 4, 4, 1, 1, which is a simple pattern. So the right number in the missing term should be 21. Step 3: Examine the letters: 11M13, 13Q17, ?, 17V22, 19W23. M is the 13th letter, matching the right number 13. Q is the 17th letter, matching the right number 17. V is the 22nd letter, matching the right number 22. W is the 23rd letter, matching the right number 23. Step 4: Recognise the rule: the letter position equals the right-hand number in each term. Step 5: The right-hand number in the missing term is 21, so the letter must be the 21st letter, which is U. Step 6: Hence, the missing term is 15U21. Verification / Alternative check: Rewriting the complete series as 11M13, 13Q17, 15U21, 17V22, 19W23 we see: left numbers form an arithmetic progression with common difference 2; right numbers grow as 13, 17, 21, 22, 23; and the letter in each term is exactly the right number's alphabetical position. This triple consistency strongly confirms that 15U21 is the correct term. Why Other Options Are Wrong: 15R18 and 15S19 use incorrect right numbers and letters. 15T20 uses 20 as the right number and T(20) as the letter, which would maintain the letter rule but break the smooth 13, 17, 21, 22, 23 structure for the right numbers. Among the options, only 15U21 satisfies all parts of the pattern at once. Common Pitfalls: Learners may try to relate the letter to an average of the two numbers or to the left number, which creates more complicated or inconsistent patterns. Another error is to guess a term that fits only one side (left or right) while ignoring the other. Always check that both the left and right numbers and the letter are all simultaneously consistent with the inferred rule. Final Answer: The term that correctly completes the number and letter pattern is 15U21.

Question 15

In the sum 8 + ?8 + 28 + 83 + 8? = 2?8, the same digit replaces each question mark. Which digit should ? represent so that the equation holds true?

Accepted Answer

Introduction / Context: This question is a classic missing digit puzzle where a single unknown digit ?, used in several positions, must be determined so that an arithmetic equation balances. The expression contains both two digit and three digit numbers formed with ?, and the same digit appears in every question mark. Our goal is to translate this into an algebraic equation and solve it consistently. Given Data / Assumptions: The expression is 8 + ?8 + 28 + 83 + 8? = 2?8. The symbol ? stands for the same digit (0–9) in every place where it appears. ?8 is a two digit number with tens digit = ? and ones digit = 8. 8? is a two digit number with tens digit 8 and ones digit = ?. 2?8 is a three digit number with hundreds digit 2, tens digit = ?, and ones digit 8. Concept / Approach: We introduce a variable, say x, for the unknown digit ?. Then we express each composite number in terms of x using place value: ?8 becomes 10x + 8, 8? becomes 80 + x, and 2?8 becomes 200 + 10x + 8. Substituting these expressions into the equation converts it into a standard linear equation in x, which we can solve using ordinary algebra. Finally, we check which value of x between 0 and 9 satisfies the equation and is also a valid single digit. Step-by-Step Solution: Step 1: Let ? = x, where x is a digit between 0 and 9. Step 2: Rewrite each composite number: ?8 = 10x + 8. 8? = 80 + x. 2?8 = 200 + 10x + 8. Step 3: Substitute into the equation: 8 + (10x + 8) + 28 + 83 + (80 + x) = 200 + 10x + 8. Step 4: Collect constant terms on the left: 8 + 8 + 28 + 83 + 80 = 207. Step 5: Collect x terms on the left: 10x + x = 11x. So left side = 11x + 207. Step 6: Simplify the right side: 200 + 10x + 8 = 208 + 10x. Step 7: Set both sides equal: 11x + 207 = 208 + 10x. Step 8: Subtract 10x from both sides: 11x - 10x + 207 = 208. This gives x + 207 = 208, so x = 1. Verification / Alternative check: Substitute x = 1 back into the original expression. Then ?8 = 18, 8? = 81, and 2?8 = 218. The sum of the left side is 8 + 18 + 28 + 83 + 81. Compute step by step: 8 + 18 = 26, 26 + 28 = 54, 54 + 83 = 137, 137 + 81 = 218. This equals the right side, 218, confirming that x = 1 satisfies the equation exactly. Why Other Options Are Wrong: If ? were 2, 3 or 4, then the equation would become a different linear equation and the sum on the left would not match the number formed on the right. A quick check reveals mismatches; for example, with x = 2 we would have 28 and 82 instead, leading to a left side different from 228. Therefore, only x = 1 yields a correct and consistent equality. Common Pitfalls: Some learners may misinterpret ?8 or 8? as multiplication expressions rather than two digit numbers. Another common mistake is to try each digit by guesswork rather than setting up an equation, which is slower and more error prone. Working with place values and forming a clean algebraic equation provides a reliable method that scales to more complex puzzles. Final Answer: The digit represented by ? that makes the equation true is 1.

Question 16

In the number series 6, 6, 12, 36, 144, 720, ?, each term is generated by a consistent multiplicative rule. What is the next number in the series?

Accepted Answer

Introduction / Context: This is a multiplicative series where the numbers grow very quickly. Such sequences are often based on factorial like patterns or repeated multiplication by increasing integers. Identifying the exact multiplier at each step allows us to compute the next term without ambiguity. Given Data / Assumptions: The series is: 6, 6, 12, 36, 144, 720, ? Only one term, the last, is missing. We assume the rule is multiplicative rather than additive, given the rapid growth. The multipliers may follow their own simple sequence, such as 1, 2, 3, 4, 5, 6. Concept / Approach: We examine the ratio between successive terms to detect how each is produced from the previous one. If these ratios form a simple progression, we can extend that progression and multiply the last known term by the correct factor to get the next term. This approach is particularly effective for series whose magnitudes grow quickly. Step-by-Step Solution: Step 1: Compute the ratios of consecutive terms. 6 (second term) divided by 6 (first term) = 1. 12 divided by 6 = 2. 36 divided by 12 = 3. 144 divided by 36 = 4. 720 divided by 144 = 5. Step 2: Recognise the pattern of multipliers: ×1, ×2, ×3, ×4, ×5. Step 3: The next multiplier in this natural sequence is ×6. Step 4: Apply this multiplier to the last known term: 720 × 6 = 4320. Step 5: Therefore, the missing term is 4320. Verification / Alternative check: We can reconstruct the series explicitly: start with 6, multiply by 1 to stay at 6, then multiply by 2 to get 12, multiply by 3 to get 36, multiply by 4 to get 144, and multiply by 5 to get 720. This confirms that the multipliers are indeed the natural numbers from 1 to 5. Continuing with a multiplier of 6 yields 4320, ensuring consistency of the pattern. Why Other Options Are Wrong: Numbers like 3547, 2154 or 1765 are not equal to 720 times a small integer and do not fit any obvious extension of the multiplier sequence. They would require arbitrary, non integral or irregular multipliers that are inconsistent with the simple pattern observed so far. Thus, they cannot be part of this logically constructed series. Common Pitfalls: One mistake is to look at differences, which are irregular and do not show a simple pattern here. Another is to miscalculate one of the ratios and therefore miss the straightforward sequence of multipliers. Carefully computing each ratio and checking that they form 1, 2, 3, 4, 5 prevents these errors and makes the series easy to extend. Final Answer: Following the pattern of multiplying by 1, 2, 3, 4, 5, the next term is obtained by multiplying 720 by 6, giving 4320.

Question 17

In the series 8, 11, 19, 23, 32, ?, determine the next number that correctly continues the pattern.

Accepted Answer

Introduction / Context: This sequence alternates between relatively small and moderately larger jumps, which suggests that the differences between consecutive terms follow their own pattern in two intertwined streams. Identifying this alternating structure allows us to predict the next increment and therefore the next term accurately. Given Data / Assumptions: The series is: 8, 11, 19, 23, 32, ? We must find the next term at the end. We assume a consistent rule, likely in the pattern of differences. The differing sizes of the jumps hint at alternating small and large increments. Concept / Approach: We compute the differences between consecutive terms and then examine those differences themselves as a new sequence. If the differences alternate between two simple progressions (for example 3, 4, 5 and 8, 9, 10), we can extend the appropriate progression to find the next difference. Adding this difference to the last known term yields the next number in the original series. Step-by-Step Solution: Step 1: Compute the differences between consecutive terms. 11 - 8 = 3. 19 - 11 = 8. 23 - 19 = 4. 32 - 23 = 9. Step 2: Group the differences into two sequences: small and large. Small differences: 3, 4, ... Large differences: 8, 9, ... Step 3: Notice that the small differences increase by 1: 3 → 4, so the next small difference should be 5. Step 4: Notice that the large differences also increase by 1: 8 → 9, so the next large difference would be 10, but this is for the step after our missing term. Step 5: The pattern of differences is therefore 3, 8, 4, 9, 5, 10, ... applied alternately. Step 6: We have already used 3, 8, 4, 9; the next difference to add is 5. Step 7: Add 5 to the last known term: 32 + 5 = 37. Verification / Alternative check: Write out the extended series including the next term: 8, 11, 19, 23, 32, 37. The differences are 3, 8, 4, 9, 5. This matches the pattern 3, 8, 4, 9, 5, and if we continued, we would expect a difference of 10 next, consistent with the observed rule. The alternating sequences of small and large differences, each increasing by 1, confirm that 37 is indeed the correct extension. Why Other Options Are Wrong: If we chose 39, the new difference would be 7, which does not fit either the small (3, 4, 5, ...) or large (8, 9, 10, ...) progression. Choosing 47 or 49 produces even larger differences that do not continue either of the sub sequences. Thus those values break the carefully alternating structure that the existing terms display. Common Pitfalls: A frequent mistake is to look only at the overall growth and attempt to guess a single difference sequence, which appears irregular. Another is to consider just the first two increments and assume a simple pattern, ignoring the alternation. Looking at all differences in order and noticing the alternating small and large increases is essential for solving this type of problem correctly. Final Answer: Maintaining the alternating difference pattern of 3, 8, 4, 9, 5, 10, the next term after 32 is 37.

Question 18

In the four digit number series 6834, 6151, 5536, 4983, x, each new term is obtained by subtracting a specific three digit number from the previous term. Which option correctly gives the next term x?

Accepted Answer

Introduction / Context: This question involves a series of four digit numbers. The values decrease but not by a constant amount, which suggests that each step uses a rule based on the digits themselves rather than on a fixed difference. Recognising how the subtracted quantities relate to the digits of the current term is the key to predicting the next number in the series. Given Data / Assumptions: The series is: 6834, 6151, 5536, 4983, x. We must determine the value of x. Each term is obtained from the previous term by subtracting a three digit number. The three digit number being subtracted is likely derived from the digits of the current term. Concept / Approach: We calculate the differences between consecutive terms and then examine these differences as separate three digit numbers. If these differences are formed from the leading digits of the earlier term (for example, by concatenating the first three digits), this provides a simple, digit based rule for constructing each new term. Once we confirm this pattern, we apply it to the last known term to obtain x. Step-by-Step Solution: Step 1: Compute the differences between consecutive terms as positive three digit numbers. 6834 - 6151 = 683. 6151 - 5536 = 615. 5536 - 4983 = 553. Step 2: Express each number explicitly with its digits: First term: 6834 → leading three digits are 6, 8, 3, forming 683. Second term: 6151 → leading three digits are 6, 1, 5, forming 615. Third term: 5536 → leading three digits are 5, 5, 3, forming 553. Step 3: Observe that each difference equals the three digit number formed by the first three digits of the previous term. 6834 - 683 = 6151. 6151 - 615 = 5536. 5536 - 553 = 4983. Step 4: Apply the same rule to obtain the next term from 4983. Form the three digit number from the first three digits of 4983: that is 4, 9, 8 → 498. Step 5: Subtract this value from 4983. Compute 4983 - 498 = 4485. Step 6: Therefore, x = 4485. Verification / Alternative check: We can summarise the rule: each new term = current term minus the three digit number composed of the current term's first three digits. Starting from 6834, this gives 6834 - 683 = 6151; then 6151 - 615 = 5536; 5536 - 553 = 4983; 4983 - 498 = 4485. There is no inconsistency in this process, and the relationship holds at every step, strongly confirming that 4485 is the correct next term. Why Other Options Are Wrong: Values such as 4467, 4538 or 4184 do not equal 4983 minus 498. To obtain those, one would need to subtract different three digit numbers that do not match the pattern derived from the leading digits. Thus, they break the digit based subtraction rule that matches all earlier transitions in the series. Only 4485 preserves this structure. Common Pitfalls: It is easy to focus on numerical differences alone without relating them to the digits of the terms. Another frequent mistake is to search for constant or linearly changing differences, which do not appear here. The important insight is that the subtracted values are not arbitrary but exactly mirror the first three digits of each term. Once this is seen, predicting the next term becomes straightforward. Final Answer: Using the rule of subtracting the three digit number formed by the first three digits of each term, the next term in the series is 4485.

Question 19

Find the wrong number in the following series: 1500, 1475, 1448, 1419, 1389, 1355, 1320

Accepted Answer

Introduction / Context: This verbal reasoning question tests the candidate ability to analyse a decreasing number series and identify the single term that breaks an otherwise smooth numerical pattern. Such problems are very common in competitive exams because they check both observation and basic arithmetic skills together. Here, we are given a descending series starting from 1500, and we must decide which one of the numbers does not fit the rule that is followed by the remaining terms. Given Data / Assumptions: - Given series: 1500, 1475, 1448, 1419, 1389, 1355, 1320.- Exactly one term is incorrect, while the other terms follow a consistent pattern.- The pattern is expected to involve regular subtraction using a predictable sequence of numbers. Concept / Approach: The most natural approach in a decreasing series is to look at the differences between consecutive terms. If almost all differences follow a simple pattern (for example, odd numbers in sequence), then any term that does not respect this rule can be marked as the wrong number. We will compute the successive differences and attempt to see whether they follow a sequence of consecutive odd numbers or some other regular structure. Step-by-Step Solution: - Difference between 1500 and 1475: 1500 - 1475 = 25.- Difference between 1475 and 1448: 1475 - 1448 = 27.- Difference between 1448 and 1419: 1448 - 1419 = 29.- Difference between 1419 and 1389: 1419 - 1389 = 30.- Difference between 1389 and 1355: 1389 - 1355 = 34.- Difference between 1355 and 1320: 1355 - 1320 = 35.- We observe: 25, 27, 29 are consecutive odd numbers, and 35 is also odd and fits at the end.- A very natural and consistent rule would be to subtract consecutive odd numbers: 25, 27, 29, 31, 33, 35.- Applying this correct pattern: 1500 - 25 = 1475; 1475 - 27 = 1448; 1448 - 29 = 1419; 1419 - 31 = 1388; 1388 - 33 = 1355; 1355 - 35 = 1320.- According to this pattern, the fifth term should be 1388, but the given series has 1389 instead. Verification / Alternative check: - Check all other terms: 1500, 1475, 1448, 1419, 1355 and 1320 all match perfectly with the rule of subtracting consecutive odd numbers 25, 27, 29, 33 and 35 from their immediate predecessors.- Only the step from 1419 to 1389 breaks this pattern, because the correct subtraction should be 1419 - 31 = 1388.- Therefore, 1389 is the unique term that does not fit the consistent logic of the series. Why Other Options Are Wrong: - 1475 fits the rule because 1500 - 25 = 1475; it is consistent.- 1419 fits because 1448 - 29 = 1419; it matches the expected subtraction.- 1355 fits because 1388 (corrected term) - 33 = 1355; the difference is an odd number in the sequence.- 1320 fits because 1355 - 35 = 1320, again respecting the consecutive odd-number pattern. Common Pitfalls: - Some candidates only check approximate differences and may mistakenly mark an endpoint like 1320 without fully verifying the complete pattern.- Another mistake is to assume a fixed difference, such as subtracting a constant number, instead of recognising a growing sequence of odd differences.- Ignoring one of the middle differences or miscalculating just one subtraction can easily lead to the wrong answer. Final Answer: The only term that violates a clear pattern of subtracting consecutive odd numbers from left to right is 1389, so 1389 is the wrong number in the series.

Question 20

What number should replace the question mark in the series: 1050, 420, 168, 67.2, ?

Accepted Answer

Introduction / Context: This question checks understanding of number series based on repeated multiplication by a constant factor. Reasoning questions of this type are extremely common in aptitude tests because they require candidates to recognise patterns involving fractions and decimal multipliers, not just simple addition or subtraction. Here, we must decide which number should replace the question mark to continue the series logically. Given Data / Assumptions: - Given series: 1050, 420, 168, 67.2, ?- Exactly one value is missing, represented by a question mark.- All terms are real numbers and can include decimals.- We expect a single consistent rule operating between consecutive terms. Concept / Approach: The natural approach is to check the ratio between each pair of consecutive terms. If the ratios are approximately equal, the series is multiplicative. The presence of decimal values like 67.2 suggests a fractional multiplier such as 0.4 or 2.5. Once we discover the common ratio, we can apply it to the last known term to find the missing value. Step-by-Step Solution: - Compute the ratio from 1050 to 420: 420 / 1050 = 0.4.- Compute the ratio from 420 to 168: 168 / 420 = 0.4.- Compute the ratio from 168 to 67.2: 67.2 / 168 = 0.4.- The common ratio between all consecutive terms is therefore 0.4.- To obtain the missing term, multiply the last known term by the same factor: 67.2 * 0.4.- Calculation: 67.2 * 0.4 = 26.88.- Thus, the missing number that continues the series is 26.88. Verification / Alternative check: - We can rewrite the complete series using the discovered rule: 1050, 1050 * 0.4 = 420, 420 * 0.4 = 168, 168 * 0.4 = 67.2, and 67.2 * 0.4 = 26.88.- The factor 0.4 is equal to 2 / 5, so the series is equivalent to repeatedly taking two fifths of the previous term.- There is no inconsistency once we include 26.88 as the fifth term, confirming that it is the correct answer. Why Other Options Are Wrong: - 19.11, 14.25, 10.752 and 8.64 do not equal 67.2 multiplied by 0.4 and would break the constant-ratio pattern.- Using any of these values would make the series ratios unequal, which contradicts the clear multiplicative structure from the first three transitions. Common Pitfalls: - Some candidates look for differences instead of ratios and may attempt to treat this as an additive series, which quickly leads to confusion because the differences are not constant.- Rounding errors while computing decimal ratios can cause incorrect guesses when the exact factor 0.4 is not recognised.- Ignoring the clear pattern in the first three transitions and only attempting to fit the given options can also be misleading. Final Answer: The only value that maintains a constant multiplicative factor of 0.4 between all consecutive terms is 26.88, so 26.88 is the correct number to replace the question mark.

Number Series Questions