Question 1

What number should replace the question mark in the series 38, 195, ?, 4905, 24530, 122655?

Accepted Answer

Introduction / Context: This number series question involves rapidly increasing values that suggest a multiplicative pattern. The challenge is to detect the specific operation used at each step and then apply it to find the missing term. Given Data / Assumptions: Partial series: 38, 195, ?, 4905, 24530, 122655. Exactly one term in the middle is missing. The series appears to grow roughly by a factor of about five each time. Concept / Approach: Since the numbers grow quite quickly, start by checking whether each term relates to the previous term via a constant multiplier or a simple linear expression such as multiplying by a fixed number and then adding or subtracting a small constant. Step-by-Step Solution: Step 1: Examine the relation between the first two terms: 38 to 195. Step 2: Compute 38 * 5 = 190, and 190 + 5 = 195. So 195 = 38 * 5 + 5. Step 3: Assume the same rule applies: term_{n+1} = term_n * 5 + 5. Step 4: Let the missing term be X. Then X should be 195 * 5 + 5. Step 5: Calculate 195 * 5 = 975 and 975 + 5 = 980, so X = 980. Step 6: Check from X to the next known term: 980 * 5 + 5 = 4900 + 5 = 4905 which matches the series. Step 7: Continue for completeness: 4905 * 5 + 5 = 24525 + 5 = 24530; 24530 * 5 + 5 = 122650 + 5 = 122655. The rule holds throughout. Verification / Alternative check: By rebuilding the series with the rule term_{n+1} = term_n * 5 + 5, we get the full list: 38, 195, 980, 4905, 24530, 122655. Every step is consistent, so there is no contradiction. This confirms that 980 is the only value that keeps the pattern intact. Why Other Options Are Wrong: If we choose 885, 824, or 1021, the relation term_{n+1} = term_n * 5 + 5 fails at one or more positions. The products and sums no longer match the given terms 4905, 24530, or 122655, so those options break the series rule. Common Pitfalls: A typical mistake is to approximate the factor as 4 or 6 because of mental rounding, which leads to inconsistent patterns and incorrect answers. Another pitfall is to forget the constant addition after multiplication and check only for pure multiples of 5. Always verify the pattern across multiple adjacent terms. Final Answer: The missing number that correctly completes the series is 980.

Question 2

Find the missing term in the series 2, 3, 6, 15, ?, 157.5.

Accepted Answer

Introduction / Context: This problem involves a multiplicative number series where the multiplying factor itself changes according to a simple pattern. Recognising this pattern is the key to identifying the missing term. Given Data / Assumptions: Series: 2, 3, 6, 15, ?, 157.5. Exactly one term in the middle is missing. Decimal result at the end suggests fractional multipliers. Concept / Approach: To solve this, we examine the ratio between consecutive terms to see whether there is a sequence of multipliers with a regular increment or decrement. Since the numbers grow quite quickly but not as fast as a pure geometric progression with a fixed ratio, we suspect that the multiplier itself is changing gradually. Step-by-Step Solution: Step 1: Find the factor from 2 to 3: 3 / 2 = 1.5. Step 2: From 3 to 6 the factor is 6 / 3 = 2. Step 3: From 6 to 15 the factor is 15 / 6 = 2.5. Step 4: The multipliers so far are 1.5, 2.0, 2.5, suggesting that each time the factor increases by 0.5. Step 5: The next multiplier should therefore be 3.0. Step 6: Apply this to the known term 15: 15 * 3 = 45, so the missing term is 45. Step 7: Check the factor from 45 to 157.5: 157.5 / 45 = 3.5, which continues the pattern of multipliers 1.5, 2.0, 2.5, 3.0, 3.5. Verification / Alternative check: Rewriting the entire series with the discovered rule yields: start with 2, then multiply successively by 1.5, 2, 2.5, 3, and 3.5. This results in 2, 3, 6, 15, 45, 157.5. Every step fits the established sequence of increasing multipliers, which confirms the answer. Why Other Options Are Wrong: Values like 87, 78.5, or 56.5 break the smooth pattern of multipliers increasing by 0.5. For example, if the missing term were 87, then 87 / 15 is 5.8 which does not fit the half step pattern, and 157.5 / 87 is also inconsistent. Therefore those values cannot maintain the intended rule. Common Pitfalls: Many learners look only for integer multipliers or fixed ratios and may give up when they see decimals. Others try to force an additive pattern even when the numbers grow too rapidly for that to make sense. Always be ready to consider fractional multipliers and check whether the changes in the multiplier follow a simple progression. Final Answer: The missing term that continues the increasing half step multiplier pattern is 45.

Question 3

What is the next number in the series 3, 5, 8, 15, 28, 51, ?

Accepted Answer

Introduction / Context: This number series problem is more challenging because the pattern in the differences is not straightforward like a simple arithmetic progression. It uses the idea of adding prime numbers related to each term, which makes it a good test of logical observation and basic number theory. Given Data / Assumptions: Series: 3, 5, 8, 15, 28, 51, ? We must find the next term that continues the same hidden rule. All terms are positive integers. Concept / Approach: When simple differences do not form a clear pattern, it can be useful to ask whether some special kind of numbers, such as primes, squares, or cubes, are involved. Here, the idea is that each new term is formed by adding the largest prime number less than the current term. Step-by-Step Solution: Step 1: Start with 3. The largest prime less than 3 is 2. So next term = 3 + 2 = 5. Step 2: For 5, the largest prime less than 5 is 3. Next term = 5 + 3 = 8. Step 3: For 8, the primes less than 8 are 2, 3, 5, 7. The largest prime less than 8 is 7. Next term = 8 + 7 = 15. Step 4: For 15, the primes less than 15 are 2, 3, 5, 7, 11, 13. The largest is 13. Next term = 15 + 13 = 28. Step 5: For 28, the primes less than 28 include 23. The largest prime less than 28 is 23. Next term = 28 + 23 = 51. Step 6: For 51, the primes less than 51 include 47 as the largest prime below 51. So the next term = 51 + 47 = 98. Verification / Alternative check: We can confirm the rule systematically by listing the largest prime less than each term and checking that adding it produces the next term. The sequence of primes added is 2, 3, 7, 13, 23, 47. Each step matches the given terms exactly, and 51 + 47 produces 98, which is one of the provided options. No other number in the options can be produced by this consistent rule. Why Other Options Are Wrong: Values 102, 87, or 79 do not satisfy the pattern of adding the largest prime less than the current term. For example, 102 would require adding 51, which is not prime. Similarly, 87 and 79 would require adding composite numbers or primes that are not the largest below 51. Hence these cannot continue the pattern. Common Pitfalls: Many students look only at first differences (2, 3, 7, 13, 23) and try to force a pattern there, which is hard to see without noticing that they are all primes. Another pitfall is to assume that an irregular series has no clear rule and resort to guessing. In advanced series questions, always consider whether primes or other special sets of numbers might be driving the pattern. Final Answer: The next term in the series, obtained by adding the largest prime less than 51, is 98.

Question 4

In the series 18, 37, 76, 155, 314, 635, which number is the odd one out?

Accepted Answer

Introduction / Context: This is an odd man out question based on a number series where the step sizes between terms grow rapidly according to a rule. The task is to find a consistent pattern among most of the terms and then identify the term that does not belong. Given Data / Assumptions: Series: 18, 37, 76, 155, 314, 635. Exactly one term is incorrect or does not follow the series rule. The pattern appears to involve doubling and adding a small constant. Concept / Approach: In series where the numbers grow quite fast but not purely geometrically, check differences between terms. If those differences themselves follow a regular rule, such as doubling and then adding one, you can identify the intended pattern and then see where it breaks. Step-by-Step Solution: Step 1: Compute the differences: 37 − 18 = 19, 76 − 37 = 39, 155 − 76 = 79, 314 − 155 = 159, 635 − 314 = 321. Step 2: Observe the first four differences: 19, 39, 79, 159. Each term is almost double the previous one plus 1. Step 3: Check: 19 * 2 + 1 = 39, 39 * 2 + 1 = 79, 79 * 2 + 1 = 159. The pattern is consistent for these. Step 4: Continue the rule: the next difference should be 159 * 2 + 1 = 318 + 1 = 319. Step 5: Add this to 314 to get the next correct term: 314 + 319 = 633. Step 6: The series therefore should be 18, 37, 76, 155, 314, 633. The given term 635 does not match this value and is off by 2. Verification / Alternative check: With the corrected last term 633, the difference pattern 19, 39, 79, 159, 319 is perfectly consistent and follows difference_{n+1} = 2 * difference_n + 1. No other correction aligns with such a simple rule, so the logical conclusion is that 635 is the erroneous term. Why Other Options Are Wrong: If we remove 37, 155, or 314, the remaining series cannot be made to fit the clean difference doubling plus one pattern. For example, without 155 the transition between 76 and 314 does not fit the rule. Hence only 635 stands out as the incorrect term. Common Pitfalls: Learners sometimes check only the original numbers and miss the structure in the differences. Another error is to try multiplicative rules directly on the main terms, which here would produce ratios that are not as simple as the difference pattern. For series questions, always check both differences and ratios, and prefer the explanation that is simple and consistent across the longest stretch of terms. Final Answer: The number that does not fit the intended pattern is 635.

Question 5

In the series 12, 16, 32, 68, ?, find the missing term.

Accepted Answer

Introduction / Context: This number series problem relies on recognising a pattern in the differences between consecutive terms. The differences here turn out to follow a regular progression that grows steadily, making this a classic aptitude question. Given Data / Assumptions: Series: 12, 16, 32, 68, ? Exactly one term is missing. The rule that generates each new term is consistent across the series. Concept / Approach: When there is no obvious multiplicative pattern, it is standard practice to look at the first-level differences. If those differences themselves follow an arithmetic progression or some other simple rule, we can extend that pattern to determine the next difference and hence the next term. Step-by-Step Solution: Step 1: Compute differences: 16 − 12 = 4, 32 − 16 = 16, 68 − 32 = 36. Step 2: Look at these differences: 4, 16, 36. Notice that 4 = 2^2, 16 = 4^2, 36 = 6^2. They are squares of even numbers 2, 4, and 6. Step 3: This suggests that the next difference may be 8^2 = 64, continuing the pattern of even squares 2^2, 4^2, 6^2, 8^2. Step 4: Add this difference to the last known term: 68 + 64 = 132. Verification / Alternative check: With the candidate term 132, the series becomes 12, 16, 32, 68, 132. The differences are 4, 16, 36, 64 which correspond to 2^2, 4^2, 6^2, 8^2. The pattern of square numbers of consecutive even integers is clean and consistent, confirming that 132 is correct. Why Other Options Are Wrong: Options 198, 164, and 118 yield differences that do not fit the even square pattern. For instance, if the term were 164, the last difference would be 96, which is not a perfect square. These choices would destroy the simple structure observed in the first three differences. Common Pitfalls: A frequently seen mistake is to search for a direct formula on the main terms and ignore the pattern in the differences. Another error is to assume the differences are random or only linear, whereas in many exam series they are derived from squares or cubes. Taking the time to check for perfect squares and cubes in differences often reveals the intended pattern quickly. Final Answer: The missing term that preserves the even square difference pattern is 132.

Question 6

Find the missing number in the series 1, 6, 15, ?, 45, 66, 91.

Accepted Answer

Introduction / Context: This is a classic number series question where each term increases by a changing amount. The sequence of differences follows a simple arithmetic pattern, and recognising this pattern allows us to fill in the missing value. Given Data / Assumptions: Series: 1, 6, 15, ?, 45, 66, 91. Exactly one term in the middle is missing. The rule governing the series is the same throughout. Concept / Approach: The first step is to compute differences between known neighbouring terms. In many aptitude series, these differences form a simple arithmetic progression, even when the original terms do not. Once that progression is identified, the missing term can be reconstructed. Step-by-Step Solution: Step 1: Compute some known differences using terms with no gap at both ends: 66 − 45 = 21 and 91 − 66 = 25. Step 2: Also compute the first two differences at the start: 6 − 1 = 5 and 15 − 6 = 9. Step 3: Consider the sequence of differences we know or expect: 5, 9, ?, 21, 25. Step 4: The pattern suggests an arithmetic progression of differences increasing by 4 each time: 5, 9, 13, 17, 21, 25. Step 5: So the missing difference between the third and fourth terms should be 13, and the next difference should be 17 between the fourth and fifth terms. Step 6: From the third term 15, add 13 to get the fourth term: 15 + 13 = 28. Step 7: Check that from this fourth term we can reach 45 with a difference of 17: 28 + 17 = 45, which is already in the series. Verification / Alternative check: With the missing number set to 28, the complete series is 1, 6, 15, 28, 45, 66, 91. The differences are 5, 9, 13, 17, 21, 25 which clearly form an arithmetic progression with common difference 4. This confirms that the pattern is correct and that 28 is the only value that fits consistently. Why Other Options Are Wrong: If we choose 24, 26, or 32, the resulting differences fail to follow the steady increase of 4. For example, with 24, the difference from 15 is 9 and from 24 to 45 is 21, which breaks the smooth 5, 9, 13, 17, 21, 25 sequence. Therefore these options cannot be correct. Common Pitfalls: Students sometimes try to relate each term directly to the previous one through multiplication or squaring, which complicates what is actually a simple pattern in differences. Another pitfall is to look only at part of the series and overlook the later differences, which contain strong clues. Always consider all available terms when extracting the pattern. Final Answer: The missing number that preserves the increasing difference pattern is 28.

Question 7

In the series 114, 131, 165, 216, ?, 369, what number should replace the question mark?

Accepted Answer

Introduction / Context: This question involves a number series where the jumps between terms are not constant but follow a secondary pattern. The focus is on recognising an arithmetic progression in the differences between consecutive terms. Given Data / Assumptions: Series: 114, 131, 165, 216, ?, 369. Exactly one term between 216 and 369 is missing. The same rule applies to all steps in the series. Concept / Approach: We start by computing differences between known adjacent terms. If those differences themselves grow in a regular way, such as forming an arithmetic progression, that pattern can be extended to locate the missing term. Step-by-Step Solution: Step 1: Compute differences for the known parts: 131 − 114 = 17. Step 2: Next difference: 165 − 131 = 34. Step 3: Next difference: 216 − 165 = 51. Step 4: Observe that 17, 34, and 51 form a pattern where each difference increases by 17: 34 − 17 = 17 and 51 − 34 = 17. Step 5: Following this rule, the next difference should be 51 + 17 = 68. Step 6: Add this to the last known term: missing term = 216 + 68 = 284. Step 7: To confirm, check the final difference: 369 − 284 = 85, which is again 68 + 17, continuing the same pattern. Verification / Alternative check: With the missing term set to 284, the series becomes 114, 131, 165, 216, 284, 369. The differences are 17, 34, 51, 68, 85. This is an arithmetic progression of differences where each difference increases by 17. The rule fits every step, confirming that 284 is the correct value. Why Other Options Are Wrong: If we insert 294, 304, or 314, the last two differences do not form a difference sequence that increases by a constant 17. For example, with 294, the differences would be 17, 34, 51, 78, 75, which destroys the linear pattern. Hence those options cannot be correct. Common Pitfalls: One pitfall is to assume that the main series itself is an arithmetic progression and look for a constant difference, which clearly does not work here. Another mistake is to stop after noticing that the differences roughly increase and not to compute the exact increments, which are crucial in this question. Always compute all differences carefully to find the precise pattern. Final Answer: The number that correctly completes the series is 284.

Question 8

In the series 2880, 480, 92, 24, 8, 4, 4, which term is wrong?

Accepted Answer

Introduction / Context: This is an odd term detection question in a descending series that appears to involve division by successively smaller integers. The task is to reconstruct the intended pattern and identify which term does not fit. Given Data / Assumptions: Series: 2880, 480, 92, 24, 8, 4, 4. Exactly one term is incorrect. The series is expected to follow a neat division rule. Concept / Approach: When a series decreases significantly from term to term, it often involves division by an integer factor. A typical pattern is division by 6, then by 5, then by 4, then by 3, then by 2, then by 1. We can test whether this structure applies. Step-by-Step Solution: Step 1: Check the first two terms: 2880 / 6 = 480. So a natural first step is division by 6. Step 2: Next, if we divide by 5: 480 / 5 = 96, but the series gives 92. This suggests 92 is suspicious. Step 3: Continue the hypothetical correct pattern: from 96 divide by 4 to get 96 / 4 = 24, which matches the next term. Step 4: Then divide by 3: 24 / 3 = 8, which matches the next term. Step 5: Next divide by 2: 8 / 2 = 4, again matching the series. Step 6: Finally, division by 1 keeps the last term as 4, so the final 4 is also consistent. Step 7: Therefore, the only incorrect term is 92, which should have been 96 to follow the division pattern by 6, 5, 4, 3, 2, and 1. Verification / Alternative check: If we rewrite the corrected series as 2880, 480, 96, 24, 8, 4, 4, the operations between terms are: divide by 6, divide by 5, divide by 4, divide by 3, divide by 2, then divide by 1. This is a clear and elegant rule and uses each integer from 6 down to 1 exactly once. The given term 92 is the only one that breaks this pattern. Why Other Options Are Wrong: 480, 24, and 4 all fit perfectly in the division chain. If any of them were replaced, we could not retain the simple successive division rule. Only 92 fails to equal the expected result of 480 divided by 5. Common Pitfalls: Candidates might incorrectly attempt subtraction or mixed operations and end up with complicated schemes. Another pitfall is to accept near matches like 92 instead of noticing that 96 would make the pattern perfect. In number series questions, patterns that use consecutive integers as divisors or multipliers are very common, so they are worth checking first. Final Answer: The wrong term in the given series is 92.

Question 9

Find the next number in the series 5, 25, 61, 113, ... .

Accepted Answer

Introduction / Context: This number series question involves a steadily increasing sequence where the gaps between terms grow according to a simple rule. The pattern in the first differences is the key to identifying the next number. Given Data / Assumptions: Series: 5, 25, 61, 113, ... We need to find the next term after 113. The same rule generates each new term from the previous one. Concept / Approach: When dealing with a moderately fast growing sequence that does not appear purely geometric, we examine the differences between consecutive terms. If these differences follow a simple arithmetic progression, we can extend that to get the next difference and hence the missing term. Step-by-Step Solution: Step 1: Compute the differences: 25 − 5 = 20, 61 − 25 = 36, 113 − 61 = 52. Step 2: Look at the difference sequence: 20, 36, 52. Step 3: Compute the differences between these differences: 36 − 20 = 16, 52 − 36 = 16. Step 4: The second-level differences are constant at 16, which indicates that the first-level differences form an arithmetic progression with common difference 16. Step 5: Therefore the next difference should be 52 + 16 = 68. Step 6: Add this to the last known term: next term = 113 + 68 = 181. Verification / Alternative check: With the candidate next term 181, the extended series is 5, 25, 61, 113, 181. The differences are now 20, 36, 52, 68. The second-level differences remain 16, 16, 16, so the pattern is fully consistent. No other option maintains this simple second-level arithmetic progression. Why Other Options Are Wrong: If we choose 142, 156, or 179, the resulting difference from 113 does not equal 68, and the second-level differences no longer stay at 16. Each of those choices produces a break in the smooth progression of the first-level differences, so they cannot be correct. Common Pitfalls: A common mistake is to look only at the first differences and not consider second-level differences when the first ones do not form a simple pattern at first glance. Another error is to try to fit an ad hoc formula rather than exploiting the clean arithmetic progression present in the differences. Always remember that constant second differences are a strong clue to a quadratic type pattern. Final Answer: The next number in the series is 181.

Question 10

Complete the missing number in the series 5, 20, 76, ?, 448.

Accepted Answer

Introduction / Context: This number series question involves a pattern where each term is generated from the previous one using both multiplication and subtraction. The consistent use of these two operations with the same number is the key to solving the problem. Given Data / Assumptions: Series: 5, 20, 76, ?, 448. Exactly one middle term is missing. The rule should be uniform throughout the series. Concept / Approach: We suspect that each term is obtained by multiplying the previous term by some integer and then subtracting that same integer. This is a common pattern in number series questions. We can test this hypothesis using the known terms. Step-by-Step Solution: Step 1: From 5 to 20, check if we can express 20 as 5 * k − k for some k. Step 2: Try k = 5: 5 * 5 − 5 = 25 − 5 = 20, which matches the series. So the rule here is multiply by 5 then subtract 5. Step 3: Assume this rule continues: term_{n+1} = term_n * k − k, where k decreases by 1 each time: 5, 4, 3, 2, and so on. Step 4: From 20 to 76, check k = 4: 20 * 4 − 4 = 80 − 4 = 76, which fits. Step 5: For the missing term X, use k = 3: X = 76 * 3 − 3 = 228 − 3 = 225. Step 6: From X to 448, use k = 2: 225 * 2 − 2 = 450 − 2 = 448, which matches the given last term. Verification / Alternative check: Reconstructing the entire series with the rule term_{n+1} = term_n * k − k and k values 5, 4, 3, 2 gives: 5, 20, 76, 225, 448. Each step is consistent with the pattern: 5 * 5 − 5 = 20, 20 * 4 − 4 = 76, 76 * 3 − 3 = 225, 225 * 2 − 2 = 448. This confirms that 225 is the correct missing number. Why Other Options Are Wrong: Choosing 185, 415, or 232 would break the pattern. For example, if the missing term were 232, then the relation 76 * 3 − 3 = 232 would not hold, and 232 * 2 − 2 would not equal 448. Therefore none of these alternatives maintain a consistent descending k pattern. Common Pitfalls: One pitfall is to look for a single fixed multiplier and ignore the possibility that both multiplication and subtraction might be in play. Another is not noticing that the value subtracted is the same as the multiplier, which simplifies the rule significantly. Always test simple combined operations like k times previous minus k or plus k. Final Answer: The missing number that completes the series correctly is 225.

Question 11

In the series 6, 15, 35, 63, 143, 221, 323, only one number is wrong. Identify the wrong number.

Accepted Answer

Introduction / Context: This odd man out question is based on a series where most terms are products of consecutive prime numbers. Recognising this prime factorisation pattern allows us to identify the term that does not fit. Given Data / Assumptions: Series: 6, 15, 35, 63, 143, 221, 323. Exactly one number is incorrect or does not follow the underlying rule. The rule likely involves prime numbers and multiplication. Concept / Approach: Since the numbers are not in a simple arithmetic or geometric progression, we consider factorisation. A common competitive exam pattern is a sequence of products of consecutive primes such as 2 * 3, 3 * 5, 5 * 7, and so on. We can test each term against this idea. Step-by-Step Solution: Step 1: Factorise 6: 6 = 2 * 3, which are consecutive primes. Step 2: Factorise 15: 15 = 3 * 5, again consecutive primes. Step 3: Factorise 35: 35 = 5 * 7, consecutive primes. Step 4: Factorise 63: 63 = 7 * 9, but 9 is not a prime, so this term breaks the pattern of consecutive prime products. Step 5: Factorise 143: 143 = 11 * 13, consecutive primes. Step 6: Factorise 221: 221 = 13 * 17, consecutive primes. Step 7: Factorise 323: 323 = 17 * 19, consecutive primes. Step 8: The correct term in place of 63 should have been 7 * 11 = 77 to continue the chain 2*3, 3*5, 5*7, 7*11, 11*13, 13*17, 17*19. Verification / Alternative check: If we replace 63 with 77, the full corrected series becomes 6, 15, 35, 77, 143, 221, 323. Each term now is the product of two consecutive prime numbers: 2*3, 3*5, 5*7, 7*11, 11*13, 13*17, 17*19. No other single change yields such a clean and consistent pattern, so the identification is clear. Why Other Options Are Wrong: The terms 35, 143, and 323 all factorise into products of consecutive primes: 35 = 5 * 7, 143 = 11 * 13, 323 = 17 * 19. Removing any of these would spoil the consecutive prime product chain. Only 63 fails this test because its factorisation 7 * 9 involves a non prime factor. Common Pitfalls: Students may initially search for arithmetic or geometric patterns in the raw numbers and overlook factorisation. Another common mistake is to factor only some terms and stop early without noticing the full sequence of prime pairs. In series involving moderate sized composite numbers, checking for prime factor patterns is often a powerful strategy. Final Answer: The only number that does not follow the product of consecutive primes pattern is 63.

Question 12

The sequence begins with 1, 4, 27, ... . What are the next two numbers in this sequence?

Accepted Answer

Introduction / Context: This question tests your understanding of number sequences based on patterns of powers. Many competitive exams include problems where each term is generated from its position in the sequence using exponents. Recognising such patterns quickly is a key aptitude skill. Given Data / Assumptions: - The given sequence is 1, 4, 27, ... . - All terms are positive integers. - The rule that generates the sequence is assumed to be consistent for all terms. - We need to find the next two terms that follow the same pattern. Concept / Approach: A standard idea with such sequences is to check whether the numbers can be expressed as powers, that is, a^b form with simple integer bases and exponents. Often, the position of the term in the sequence is used as either the base or the exponent. The aim is to express each given term in a meaningful pattern such as 1^1, 2^2, 3^3, and then extend this rule to find the missing terms. Step-by-Step Solution: Step 1: Write each given term in power form. 1 can be written as 1^1. 4 can be written as 2^2. 27 can be written as 3^3. Step 2: Observe the pattern of bases and exponents. In 1^1, base and exponent are both 1. In 2^2, base and exponent are both 2. In 3^3, base and exponent are both 3. Step 3: Generalise the rule. The nth term appears to be n^n. Step 4: Find the next two terms. The 4th term is 4^4 = 256. The 5th term is 5^5 = 3125. Verification / Alternative check: We can verify the consistency of the pattern by confirming that the exponents and bases always match the term number: first term 1^1, second term 2^2, third term 3^3. Extending this rule naturally gives 4^4 and 5^5, so 256 and 3125 fit the discovered pattern perfectly. There is no conflict with any given term, so the rule is reliable. Why Other Options Are Wrong: Option B (3125, 46656) starts correctly with 3125, but 46656 is 6^6, which would skip 4^4 and 5^5 and does not maintain the step by step pattern. Option C (46656, 859587) does not align with n^n for any consecutive n values and ignores the intermediate terms. Option D (None) is incorrect because we have clearly identified a consistent rule that produces valid next terms. Common Pitfalls: A common mistake is to search only for arithmetic or geometric series (constant difference or constant ratio) and overlook patterns involving powers. Another error is to jump to 3^3, 4^3, 5^3 and similar guesses without checking how the earlier terms fit. Always attempt to express numbers as simple powers and check if their indices match positions in the sequence. Careless calculation of 4^4 or 5^5 can also lead to wrong answers, so compute carefully. Final Answer: The next two numbers in the sequence are 256 and 3125.

Question 13

Consider the number series 9, 17, 11, 19, 13, ... . What are the next three numbers in this series?

Accepted Answer

Introduction / Context: This problem checks your skill with number series where two simple patterns are interleaved. Such questions appear often in aptitude tests because they test observation, pattern recognition, and the ability to separate a mixed sequence into simpler subsequences. Given Data / Assumptions: - The given terms are 9, 17, 11, 19, 13, ... . - We must find the next three numbers in this sequence. - All terms are integers and the pattern is assumed to be regular and consistent. - The series may consist of more than one interleaved pattern. Concept / Approach: A common trick in such questions is that the odd position terms form one sequence and the even position terms form another. Each subsequence often follows a simple arithmetic pattern such as adding a constant. We will separate the series into odd and even positions and look for a regular increase or decrease in each subsequence. Step-by-Step Solution: Step 1: Mark positions of the terms. Positions: 1st = 9, 2nd = 17, 3rd = 11, 4th = 19, 5th = 13. Step 2: Form the subsequence of odd positions. Odd positions: 1st, 3rd, 5th give 9, 11, 13. This is an arithmetic progression with common difference +2. So the next odd position (7th term) will be 13 + 2 = 15. Step 3: Form the subsequence of even positions. Even positions: 2nd, 4th give 17, 19. This is also an arithmetic progression with common difference +2. So the next even positions are: 6th term = 19 + 2 = 21 and 8th term = 21 + 2 = 23. Step 4: Put the terms back into the original order. Existing: 1st 9, 2nd 17, 3rd 11, 4th 19, 5th 13. Next three: 6th = 21, 7th = 15, 8th = 23. Verification / Alternative check: Check the resulting series: 9, 17, 11, 19, 13, 21, 15, 23. Odd positions are 9, 11, 13, 15 (all increase by 2). Even positions are 17, 19, 21, 23 (also increase by 2). This symmetry confirms the correctness of the logic and the answer. Why Other Options Are Wrong: Option A (17, 10, 18) breaks both arithmetic progressions and mixes inconsistent increases and decreases. Option B (19, 14, 23) does not maintain the steady +2 pattern in both subsequences. Option D (19, 13, 22) introduces values that do not fit either arithmetic progression for odd or even positions. Common Pitfalls: Many learners try to find a single pattern across all terms and do not think about splitting the series into two subsequences. Others may misidentify the common difference due to quick mental calculation. Another common mistake is to place the new terms in the wrong positions instead of respecting the alternating sequence structure. Always write positions clearly, separate the terms, and then recombine carefully. Final Answer: The next three numbers in the series are 21, 15, and 23.

Question 14

In the series 5, 15, 30, 80, 180, 540, 1080, which term is incorrect and should be considered the wrong number?

Accepted Answer

Introduction / Context: This question is from the odd man out or wrong term in series category. The goal is to detect a consistent pattern that most terms follow and then identify the term that violates that pattern. Such problems measure logical reasoning and attention to multiplicative patterns in number sequences. Given Data / Assumptions: - The sequence is 5, 15, 30, 80, 180, 540, 1080. - Exactly one term is wrong and does not follow the main pattern. - All other terms fit a simple multiplicative rule. - We need to find which term breaks that rule. Concept / Approach: In many numeric series, terms are obtained by multiplying the previous term by alternating constants, often 2 and 3. Here, the numbers grow quickly, which suggests a pattern involving repeated multiplication. We will examine ratios of consecutive terms to see whether they follow a regular pattern such as multiply by 3, then by 2, and so on. Step-by-Step Solution: Step 1: Compute ratios of consecutive terms. 15 / 5 = 3. 30 / 15 = 2. 80 / 30 ≈ 2.67 (not a simple integer factor). 180 / 80 = 2.25. 540 / 180 = 3. 1080 / 540 = 2. Step 2: Guess the intended pattern. A very natural intended pattern is multiply alternately by 3 and 2. Starting from 5, we get: 5 * 3 = 15, then 15 * 2 = 30. If we follow this, the next term should be 30 * 3 = 90, not 80. Then 90 * 2 = 180, 180 * 3 = 540, and 540 * 2 = 1080. Step 3: Identify the wrong term. Only the term 80 breaks the alternating multiply by 3, then multiply by 2 pattern. Verification / Alternative check: Construct the corrected series using the intended pattern: 5, 15, 30, 90, 180, 540, 1080. Now check the ratios: 15 / 5 = 3, 30 / 15 = 2, 90 / 30 = 3, 180 / 90 = 2, 540 / 180 = 3, 1080 / 540 = 2. The pattern multiply by 3, then by 2 repeats perfectly, confirming that 80 is the only inconsistent value. Why Other Options Are Wrong: Option A (540) fits the pattern as 180 * 3 = 540. Option B (180) is correct because 90 * 2 = 180 in the intended series. Option C (30) is also correct since 15 * 2 = 30. Option D (80) is the only number that does not equal the previous term multiplied by 3 or 2 in the correct order, so it must be the wrong term. Common Pitfalls: Students sometimes focus only on differences rather than ratios and fail to notice the multiplicative pattern. Another mistake is to accept approximate non integer ratios such as 2.67 and 2.25 and assume the question is about arbitrary growth instead of a neat alternating rule. Always test both addition and multiplication based patterns and look for the simplest consistent explanation that fits most terms. Final Answer: The wrong term in the series is 80.

Question 15

In the number series 11, 13, 30, 96, ?, what is the next term that should replace the question mark?

Accepted Answer

Introduction / Context: This is a next term in series question where each new term is built using the previous term through a mixture of multiplication and addition. Recognising such composite operations is very important for numerical reasoning tests because they combine ideas of arithmetic progressions and geometric style growth. Given Data / Assumptions: - The series is 11, 13, 30, 96, ? . - All terms are positive integers. - There is a consistent rule involving the previous term to generate the next one. - We need to choose the correct next term from the options. Concept / Approach: When numbers increase quickly, multiplication by increasing factors plus a small addition often explains the pattern. Here, we will try expressions of the form next term = current term * n + k, where n and k follow a simple rule linked to the position of the term. The observation is that multipliers 1, 2, 3, 4 combined with additions 2, 4, 6, 8 give a neat and consistent structure. Step-by-Step Solution: Step 1: Move from 11 to 13. 11 * 1 + 2 = 13. Step 2: Move from 13 to 30. 13 * 2 + 4 = 26 + 4 = 30. Step 3: Move from 30 to 96. 30 * 3 + 6 = 90 + 6 = 96. Step 4: Generalise the rule. We are multiplying by 1, 2, 3, 4 in order and adding 2, 4, 6, 8 respectively. Both the multiplier and the added value increase by 1 in each step. Step 5: Find the next term. From 96 to the next term: 96 * 4 + 8 = 384 + 8 = 392. Verification / Alternative check: Write the pattern clearly for each step: From 11 to 13: multiply by 1, add 2. From 13 to 30: multiply by 2, add 4. From 30 to 96: multiply by 3, add 6. From 96 to ? : multiply by 4, add 8. Both components, multiplier and addition, form simple sequences, so the rule is very consistent. Substituting confirms that the only possible next term using this pattern is 392. Why Other Options Are Wrong: Option A (264) could be considered if we used only multiplication by 2.75 approximately, but that does not fit earlier steps neatly. Option C (412) and Option D (459) do not arise from any simple extension of the (multiply by n, add 2n) pattern and therefore break the regular structure. Option B (392) is the only value that preserves the clearly identified rule of multiplying by 4 and adding 8 after multiplying by 1, 2, and 3 and adding 2, 4, and 6. Common Pitfalls: A typical mistake is to look only at differences between terms, which here are 2, 17, 66 and do not follow a simple pattern at first glance. Students may give up or overcomplicate the series. A better approach is to check for multiplicative relationships and then notice regular additions. Always examine both multiplication and addition together when numbers grow more than linearly. Final Answer: The next term in the series is 392.

Question 16

In the sequence 125, 138, 164, ?, 255, which number should replace the question mark to maintain the pattern?

Accepted Answer

Introduction / Context: This question involves a sequence where the increase between consecutive terms is not constant but still follows a regular pattern. Identifying a second level pattern in the differences between terms is a common technique for solving such problems in aptitude exams. Given Data / Assumptions: - The sequence is 125, 138, 164, ?, 255. - Exactly one term is missing and must be found. - The pattern is assumed to be arithmetic at the level of differences between consecutive terms. - All numbers are positive integers. Concept / Approach: When differences between consecutive terms do not remain constant but still grow in a controlled way, we often have an arithmetic progression in the differences themselves. That is, if d1, d2, d3, d4 are the differences, then d2 - d1, d3 - d2, and so on may be equal. The plan is to compute the known differences and see if they follow a simple pattern such as adding a fixed number like 13 each time. Step-by-Step Solution: Step 1: Compute known differences. From 125 to 138: difference is 138 - 125 = 13. From 138 to 164: difference is 164 - 138 = 26. Step 2: Look for a pattern in the differences. The differences are 13 and 26, which suggests multiples of 13. We can guess the next differences as 39 and 52, increasing by 13 each time. Step 3: Use the next difference to find the missing term. Next difference after 26 is 39. So missing term = 164 + 39 = 203. Step 4: Check that the last given term 255 fits the pattern. Next difference after 39 should be 52. 203 + 52 = 255, which matches the last term. Verification / Alternative check: Write the full difference pattern: 125, 138, 164, 203, 255. Differences are 13, 26, 39, 52. These differences form an arithmetic progression with first term 13 and common difference 13. This gives a very neat and regular second level pattern, confirming that 203 is the only suitable value for the missing term. Why Other Options Are Wrong: Option A (189) would give differences 13, 26, 25, which breaks the increasing by 13 pattern. Option B (197) produces differences that do not align with multiples of 13. Option C (200) also fails to give a smooth arithmetic progression in the differences. Option D (203) uniquely preserves a difference sequence of 13, 26, 39, 52, so it is the only correct choice. Common Pitfalls: Learners sometimes search only for a constant difference and abandon the question when none appears. Another mistake is to try random ratios instead of checking the pattern in differences. For sequences that grow moderately quickly, always compute first level differences and then check whether these differences themselves form a simple sequence like an arithmetic progression. Final Answer: The missing number in the sequence is 203.

Question 17

Among the numbers 708, 392, 618 and 816, which one is the odd one out?

Accepted Answer

Introduction / Context: This problem is a classic odd one out question. You are given four numbers and must identify which number does not share a common property that the other three have. Such questions improve your ability to spot hidden numerical properties quickly, such as divisibility rules or digit sum patterns. Given Data / Assumptions: - The numbers are 708, 392, 618 and 816. - Exactly one number is different from the others with respect to a simple property. - The property is expected to be something standard like divisibility by a small integer. Concept / Approach: A very efficient method with such problems is to test divisibility rules, especially divisibility by 2, 3, 5, 9 or 11. Here, all numbers are clearly even, so divisibility by 2 does not separate them. Next, checking divisibility by 3 can be done very fast using the rule that a number is divisible by 3 if the sum of its digits is divisible by 3. Step-by-Step Solution: Step 1: Check divisibility by 3 using digit sums. For 708: digit sum is 7 + 0 + 8 = 15, which is divisible by 3. For 392: digit sum is 3 + 9 + 2 = 14, which is not divisible by 3. For 618: digit sum is 6 + 1 + 8 = 15, which is divisible by 3. For 816: digit sum is 8 + 1 + 6 = 15, which is divisible by 3. Step 2: Compare the properties. 708, 618 and 816 are all divisible by 3. 392 alone is not divisible by 3. Therefore, 392 is the odd one out. Verification / Alternative check: As an additional check, divide the numbers directly by 3: 708 / 3 = 236, 618 / 3 = 206, and 816 / 3 = 272 are all integers. However, 392 / 3 gives a non integer value. This confirms the earlier conclusion based on digit sum. Why Other Options Are Wrong: Option A (708) is divisible by 3, so it shares the key property with 618 and 816. Option C (618) is also divisible by 3 and cannot be the odd one out. Option D (816) again is divisible by 3 and fits the group pattern. Option B (392) alone fails the divisibility by 3 test, so it is the correct odd one out. Common Pitfalls: Some students may try to factorise all four numbers fully, which is time consuming. Others might look for more complicated patterns such as prime factors when a simple divisibility rule is sufficient. Remember that aptitude tests favour quick recognition using simple rules. Always check basic divisibility by 2, 3, 5, 9 before moving to complex reasoning. Final Answer: The odd one out is 392.

Question 18

In the group of ordered triples 5-20-25, 10-40-50, 4-15-24 and 25-100-125, which triple is the odd one out?

Accepted Answer

Introduction / Context: This question is about recognising a proportional relationship within ordered triples of numbers. Three of the triples follow a common multiplicative rule, while one does not. This is a standard style of odd one out problem used to test understanding of ratios and simple multiplication patterns. Given Data / Assumptions: - The triples are 5-20-25, 10-40-50, 4-15-24 and 25-100-125. - Each triple is of the form a b c, where a, b and c are positive integers. - Exactly one triple does not follow the pattern satisfied by the other three. Concept / Approach: Look for a simple relationship between the three numbers in each triple. The most natural idea is that b and c are fixed multiples of a. For example, b could be 4 times a and c could be 5 times a. If three of the triples satisfy the same set of ratios and one does not, that one will be the odd one out. Step-by-Step Solution: Step 1: Check the triple 5-20-25. 20 = 4 * 5 and 25 = 5 * 5, so b = 4a and c = 5a. Step 2: Check the triple 10-40-50. 40 = 4 * 10 and 50 = 5 * 10, again b = 4a and c = 5a. Step 3: Check the triple 25-100-125. 100 = 4 * 25 and 125 = 5 * 25, once more b = 4a and c = 5a. Step 4: Check the triple 4-15-24. If the same pattern held, b should be 4 * 4 = 16 and c should be 5 * 4 = 20. Instead, b = 15 and c = 24, which are not equal to 16 and 20. Therefore, 4-15-24 does not follow the pattern. Verification / Alternative check: Rewriting the valid triples as (a, 4a, 5a) makes the pattern very clear: (5,20,25), (10,40,50) and (25,100,125) all fit this structure. The triple (4,15,24) would have to be (4,16,20) to be consistent but it is not, so it is definitely the odd one. Why Other Options Are Wrong: Option B (5-20-25) follows the b = 4a and c = 5a pattern perfectly. Option C (10-40-50) also satisfies the same proportional relationships. Option D (25-100-125) is again consistent with b = 4a and c = 5a. Option A (4-15-24) alone does not match this rule, so it is the correct odd one out. Common Pitfalls: Sometimes students compare absolute differences such as 20 - 5 or 25 - 20 without noticing the multiplicative structure. Others may check random patterns like a + b = c, which does not hold here. The key is to think in terms of ratios because many real world relationships like speed, density or scaling work multiplicatively, and exam questions mirror that idea. Final Answer: The odd triple is 4-15-24.

Question 19

In the number series 270, 261, 279, 252, 289 and 243, which one number is the odd one out based on a simple divisibility pattern?

Accepted Answer

Introduction / Context: This is an odd one out question based on divisibility properties inside a number series. All the numbers look fairly close to each other and there is no obvious arithmetic or geometric progression. In such cases, aptitude questions often hide a simple property such as divisibility by a fixed integer, which helps to separate one number from the rest. Given Data / Assumptions: The series given in the question is: 270 261 279 252 289 243 We assume that five of these numbers share a common divisibility pattern and that only one number breaks this pattern and therefore is the odd one out. Concept / Approach: A very common hidden property is divisibility by 9. A number is divisible by 9 if the sum of its digits is a multiple of 9. We will test every number in the list for divisibility by 9. The one number that is not divisible by 9, while all others are, will be the required odd term in the series. Step-by-Step Solution: Step 1: Check 270. The sum of its digits is 2 + 7 + 0 = 9, which is divisible by 9, so 270 is a multiple of 9.Step 2: Check 261. The sum of its digits is 2 + 6 + 1 = 9, so 261 is also divisible by 9.Step 3: Check 279. The sum of its digits is 2 + 7 + 9 = 18, which is divisible by 9, so 279 is a multiple of 9.Step 4: Check 252. The sum of its digits is 2 + 5 + 2 = 9, therefore 252 is divisible by 9.Step 5: Check 243. The sum of its digits is 2 + 4 + 3 = 9, so 243 is also a multiple of 9.Step 6: Check 289. The sum of its digits is 2 + 8 + 9 = 19, which is not divisible by 9, so 289 is not a multiple of 9. Verification / Alternative check: We can also express each number as 9 multiplied by another integer. For example, 270 = 9 * 30, 261 = 9 * 29, 252 = 9 * 28 and 243 = 9 * 27. Similarly 279 = 9 * 31. However 289 does not give an integer when divided by 9. This alternative view confirms that 270, 261, 279, 252 and 243 form a neat group of multiples of 9, while 289 does not belong to this group. Why Other Options Are Wrong: Numbers 270, 279 and 243 are all exact multiples of 9, just like 261 and 252. Treating any of them as the odd one out would ignore the strong and consistent divisibility pattern and would still leave 289 as the only non multiple of 9 in the list. Common Pitfalls: Learners sometimes focus on the order of the terms or try to find a complex formula relating consecutive numbers. In many odd one out problems, it is more effective to test basic number properties such as divisibility by 2, 3, 5 or 9. Here, the divisibility by 9 test quickly reveals the correct answer. Final Answer: The only number that is not divisible by 9 in this series is 289.

Question 20

In the number series 10, 21, 54, 109 and 189, one term is wrong. Which number is incorrect if the series is meant to follow a regular pattern in the differences?

Accepted Answer

Introduction / Context: This question asks you to detect the wrong term in a number series. All the terms are fairly close together and the series appears to increase in a non linear way. Often, such questions hide a simple pattern in the first differences or second differences between successive terms. The goal is to find a smooth rule that works for all but one term. Given Data / Assumptions: The series is: 10 21 54 109 189 We assume that the intended series is generated by adding regularly increasing differences, and exactly one of the given terms does not fit this intended pattern. Concept / Approach: A good starting point is to calculate the difference between consecutive terms. If these differences themselves form an arithmetic progression or follow some simple rule, then any term that breaks this rule can be identified as incorrect. Here we will check whether the differences form a simple arithmetic sequence. Step-by-Step Solution: Step 1: Compute the first differences.From 10 to 21 the difference is 21 − 10 = 11.From 21 to 54 the difference is 54 − 21 = 33.From 54 to 109 the difference is 109 − 54 = 55.From 109 to 189 the difference is 189 − 109 = 80.Step 2: Observe the first three differences: 11, 33 and 55. These differ by 22 each time: 33 − 11 = 22 and 55 − 33 = 22.Step 3: If the pattern continued, the next difference should be 55 + 22 = 77.Step 4: Therefore, the correct last term should be 109 + 77 = 186, not 189. Verification / Alternative check: The intended difference pattern is therefore 11, 33, 55, 77, a sequence where each difference increases by 22. Rebuilding the series with this pattern gives 10, 21, 54, 109 and 186. This reconstructed list is completely consistent. Since 189 does not fit this clean difference pattern, it must be the wrong entry in the original series. Why Other Options Are Wrong: If 21, 54 or 109 were wrong, it would be impossible to create a smooth arithmetic progression of differences starting from 10 and still keep the remaining terms lined up neatly. Only by changing 189 to 186 do we obtain a consistent and simple rule for all differences. Therefore these other numbers cannot reasonably be the incorrect term. Common Pitfalls: Some students try to find a direct multiplication pattern and may get stuck. For many series problems, checking first and second differences is the most reliable method. Once you notice that the first three differences form a regular pattern, it becomes much easier to spot which subsequent difference breaks the rule and leads to the wrong term. Final Answer: The number that does not fit the intended difference pattern and is therefore wrong is 189.

Odd Man Out and Series Questions