Question 1

Given the instruction "interchange the signs + and − and also interchange the numbers 4 and 8 wherever they occur in an equation", which one of the following equations will become numerically correct after making all the stated interchanges?

Accepted Answer

Introduction / Context: This problem involves a coded transformation applied to entire equations. We are told to interchange the plus and minus signs and also to interchange the numbers 4 and 8 wherever they appear. The aim is to decide which given equation will produce a true numerical statement once all of these interchanges are applied consistently to both sides of that equation. Given Data / Assumptions: We must simultaneously replace every + with − and every − with +. We must simultaneously replace every 4 with 8 and every 8 with 4. The transformation is applied to the whole equation, including both left-hand and right-hand sides. We then evaluate the transformed equation with standard arithmetic rules. Concept / Approach: The correct strategy is to apply the substitution rules carefully to each candidate equation. After transforming the equation, we compute both sides and check whether the equality holds. The option for which the transformed left-hand side and right-hand side are equal is the correct answer. All other options will result in unequal sides after the transformation, so they will not represent valid equations. Step-by-Step Solution: Consider option B: 4 - 8 + 12 = 0.Apply sign changes: minus becomes plus and plus becomes minus, so 4 - 8 + 12 becomes 4 + 8 - 12, and the right-hand side 0 stays 0.Apply number changes: every 4 becomes 8 and every 8 becomes 4, so 4 + 8 - 12 becomes 8 + 4 - 12. The right-hand side is still 0.Evaluate the transformed left-hand side: 8 + 4 - 12 = 12 - 12 = 0, which matches the right-hand side. Verification / Alternative check: If we try option A: 4 + 8 - 12 = 12, the transformation eventually leads to 8 - 4 + 12 = 12 on the left and 12 stays 12 on the right, giving 16 ≠ 12.For option C: 8 + 4 - 12 = 24, after applying the rules, the left-hand side does not evaluate to the transformed right-hand side, so it is not a correct equation.The same inconsistency occurs with option D, so only option B produces a valid equality after all substitutions. Why Other Options Are Wrong: For each of A, C and D, at least one side of the equation changes in a way that alters the balance between left and right, so numerical equality is lost after transformation.Because the transformation systematically changes both signs and specific numbers, small changes in structure of the equation can easily make the equality fail. Common Pitfalls: A frequent mistake is to apply the transformations only to the left-hand side or only to the numbers, but not to both sides in a consistent way.Another error is to attempt mental substitution too quickly and misread 4 and 8 or the positions of plus and minus signs. Final Answer: The only equation that becomes correct after all specified interchanges is 4 - 8 + 12 = 0.

Question 2

If the usual arithmetic symbols are replaced as follows: "×" means addition, "÷" means subtraction, "+" means multiplication and "−" means division, then what is the numerical value of 20 × 8 ÷ 8 − 4 + 2?

Accepted Answer

Introduction / Context: This is a coded-operations question, where each arithmetic symbol is given a new meaning. To evaluate the expression correctly, we must first decode every symbol into the real operation it now represents, and then apply the standard order of operations. Such questions check both attention to detail and fluency with operator precedence rules. Given Data / Assumptions: "×" stands for addition. "÷" stands for subtraction. "+" stands for multiplication. "−" stands for division. Expression: 20 × 8 ÷ 8 − 4 + 2. Standard precedence still applies after decoding: multiplication and division before addition and subtraction. Concept / Approach: We translate the given coded expression into a normal arithmetic expression with the correct operations. After substitution, we carefully perform division and multiplication first, followed by addition and subtraction. It is crucial not to change the order of numbers, only the meanings of the symbols between them. Step-by-Step Solution: Rewrite each symbol: "×" becomes +, "÷" becomes −, "−" becomes ÷, and "+" becomes ×.Thus, 20 × 8 ÷ 8 − 4 + 2 becomes 20 + 8 − 8 ÷ 4 × 2.Now apply precedence: compute 8 ÷ 4 × 2 first. Since division and multiplication have the same rank, we go left to right: 8 ÷ 4 = 2, then 2 × 2 = 4.Substitute this back: 20 + 8 − 4. Now evaluate from left to right: 20 + 8 = 28 and 28 − 4 = 24. Verification / Alternative check: We can recheck by writing the decoded expression explicitly as 20 + 8 - (8 / 4) * 2 to avoid confusion and confirm that 8 / 4 = 2 and 2 * 2 = 4, so the final calculation remains 20 + 8 - 4 = 24.Trying to evaluate with the old meanings of the symbols would give a completely different and incorrect result, so the decoding step is absolutely essential. Why Other Options Are Wrong: 80 or 25 would arise only if the new operator meanings were ignored or misapplied, especially if one incorrectly treats the expression as 20 × 8 = 160 and then adjusts later.A result of 5 might come from wrong grouping or mixing up the order in which multiplication and division are handled after decoding. Common Pitfalls: Students often apply the new meanings inconsistently, forgetting to change one of the symbols in the middle of the expression.Another common error is to assume that the leftmost operation must be performed first, ignoring the higher precedence of multiplication and division. Final Answer: After decoding the symbols and evaluating with correct precedence, the value of the expression is 24.

Question 3

Consider the expression 5 × 4 + 20. If the symbols "+" and "×" are interchanged and at the same time the numbers 4 and 5 are also interchanged throughout the expression, which of the following equations shows the correct new value of the expression …

Accepted Answer

Introduction / Context: This question involves a structured transformation applied to a simple arithmetic expression. We are told that the symbols "+" and "×" are interchanged and the numbers 4 and 5 are interchanged throughout the expression. The task is to determine the correct numerical result of the transformed expression and match it with the given equation options. Given Data / Assumptions: Original expression: 5 × 4 + 20. Every "+" becomes "×" and every "×" becomes "+". Every 4 becomes 5 and every 5 becomes 4. The transformation is applied only to the left-hand side expression 5 × 4 + 20. We then evaluate the new expression using the usual order of operations. Concept / Approach: We first interpret the rules carefully to avoid double counting any substitution. The natural reading is: start from the original expression 5 × 4 + 20, systematically interchange the indicated symbols and numbers, and then compute the resulting value. The correct option is the equation whose right-hand side equals this transformed value. Step-by-Step Solution: Start with 5 × 4 + 20.Interchange the symbols "+" and "×". The expression becomes 5 + 4 × 20.Now interchange the numbers 4 and 5. The 5 becomes 4 and the 4 becomes 5, giving 4 + 5 × 20.Apply order of operations: first compute 5 × 20 = 100 and then add 4. So the value is 4 + 100 = 104. Verification / Alternative check: We can verify by redoing the two substitution steps in a different mental order. If we first interchange 4 and 5, we get 4 × 5 + 20. Then interchanging "+" and "×" yields 4 + 5 × 20, which is the same final expression as before.Evaluating again gives 4 + 100 = 104, so the transformed expression is consistent and independent of the order in which we apply the two types of interchanges. Why Other Options Are Wrong: The equation 5 × 4 + 20 = 40 corresponds to treating the original expression without any transformation, since 5 × 4 + 20 = 40.The options with right-hand sides 85 or 95 come from incorrect partial substitutions or wrong arithmetic, but they do not match the correct transformed value of 104. Common Pitfalls: A common mistake is to change only the symbols or only the numbers, instead of applying both sets of transformations.Another pitfall is to ignore operator precedence and evaluate 4 + 5 × 20 as (4 + 5) × 20, which would lead to an incorrect result of 180. Final Answer: The transformed expression evaluates to 104, so the correct equation is 5 x 4 + 20 = 104.

Question 4

Insert appropriate arithmetic symbols between 5, 0, 3 and 5 so that the resulting expression equals 20, using the usual order of operations. Which set of symbols will correctly complete the equation 5 0 3 5 = 20?

Accepted Answer

Introduction / Context: This question asks you to place the correct arithmetic operations between four numbers in order to obtain a specific result. It is a test of both mental arithmetic and your understanding of how multiplication, addition and subtraction interact under operator precedence rules. You must choose the set of symbols that makes the equation evaluate exactly to 20. Given Data / Assumptions: The pattern is 5 ? 0 ? 3 ? 5 = 20. Each "?" is to be replaced by one of the symbols +, − or × as indicated by the options. Standard precedence applies: multiplication before addition and subtraction. No brackets are to be added; only operators are inserted. Concept / Approach: We examine each candidate set of symbols, insert them in order between 5, 0, 3 and 5, and then evaluate using the standard rules. Because there are relatively few options, it is efficient to test them one by one. The correct option will give exactly 20 on the left-hand side. Step-by-Step Solution: Option B proposes -, +, ×, so the expression becomes 5 − 0 + 3 × 5.Evaluate multiplication first: 3 × 5 = 15.Now the expression is 5 − 0 + 15. Compute left to right: 5 − 0 = 5, and then 5 + 15 = 20.Thus, 5 − 0 + 3 × 5 = 20, so option B satisfies the equation. Verification / Alternative check: Option A, with ×, ×, ×, gives 5 × 0 × 3 × 5 = 0, because anything multiplied by zero becomes zero.Option C, with ×, +, ×, yields 5 × 0 + 3 × 5 = 0 + 15 = 15, which is not 20.Option D, with +, −, ×, yields 5 + 0 − 3 × 5 = 5 + 0 − 15 = −10, which is also incorrect. Why Other Options Are Wrong: Any choice that includes multiplication by zero at the start, such as option A or C, immediately forces the product part of the expression to zero, making it impossible to reach the required value 20 without additional terms.Option D fails because the negative contribution from 3 × 5 dominates, leading to a negative result rather than the positive target. Common Pitfalls: One common mistake is to ignore operator precedence and treat the expression strictly left to right. For example, misreading 5 − 0 + 3 × 5 as (5 − 0 + 3) × 5 gives 40 instead of 20.Another pitfall is to underestimate the effect of multiplying by zero, which immediately wipes out any product term in which it appears. Final Answer: The correct set of symbols is minus, plus, and multiplication in that order, so the answer is -, +, x.

Question 5

If the symbols are redefined as follows: "×" means division, "−" means multiplication, "÷" means addition and "+" means subtraction, then what is the value of (3 − 15 ÷ 19) × 8 + 6 under these new meanings?

Accepted Answer

Introduction / Context: This is another coded-operations problem in which arithmetic symbols do not carry their usual meanings. Instead, each symbol represents a different basic operation. To obtain the correct numerical value of the expression, we must first translate the entire expression into one using the standard operations, and then evaluate it carefully with the usual precedence rules. Given Data / Assumptions: "×" means division. "−" means multiplication. "÷" means addition. "+" means subtraction. Expression: (3 − 15 ÷ 19) × 8 + 6. Brackets retain their usual role of forcing inner evaluation first. Concept / Approach: The bracketed part must be decoded and evaluated first. Every symbol is replaced according to the new definitions, not according to its usual meaning. After decoding, we obtain an expression entirely in terms of standard operations, which we can compute using the normal order of operations. Finally, we compare the result with the answer choices. Step-by-Step Solution: Decode "−" as multiplication and "÷" as addition inside the bracket. So 3 − 15 ÷ 19 becomes 3 × 15 + 19.Evaluate 3 × 15 = 45, then 45 + 19 = 64, so the bracket (3 − 15 ÷ 19) represents 64.Next, the outer "×" stands for division, so (3 − 15 ÷ 19) × 8 becomes 64 ÷ 8 = 8.Finally, the symbol "+" stands for subtraction, so 8 + 6 means 8 − 6, which equals 2. Verification / Alternative check: We can rewrite the fully decoded expression as (3 * 15 + 19) / 8 - 6 to make sure there is no confusion about the operations.Evaluating again: 3 * 15 = 45, 45 + 19 = 64, then 64 / 8 = 8, and 8 - 6 = 2, which confirms the answer. Why Other Options Are Wrong: A result of 8 would come from stopping the evaluation after dividing by 8 and forgetting that the final "+" actually means subtraction.Values like 4 or −1 generally arise if one of the symbols is misinterpreted, for example reading "+" as normal addition or treating "×" as multiplication instead of division. Common Pitfalls: The most common mistake is to apply the new meanings only partially, so that some symbols are decoded and others are still interpreted in the usual way.Another pitfall is to forget the precedence of operations after decoding, particularly when brackets and multiple operations such as addition and multiplication are combined. Final Answer: After decoding all symbols and following the correct order of operations, the value of the expression is 2.

Question 6

Complete the following number analogy by finding the missing term: 12 : 30 :: 14 : ?

Accepted Answer

Introduction / Context: This is a simple number analogy question. The pair 12 : 30 is given, and we are asked to complete the analogous pair 14 : ?. To solve such questions, we have to identify the numerical relationship that links the first number in the pair with the second and then apply the same relationship to the new first number to find the missing second number. Given Data / Assumptions: First pair: 12 and 30. Second pair: 14 and an unknown number. We assume a simple arithmetic or proportional relationship between the numbers in each pair. Concept / Approach: A very common pattern in such analogies is a simple ratio or proportion between the two numbers in each pair. We examine whether 12 and 30 form a ratio that can be preserved when we move to 14 and the unknown number. Specifically, we test if the pair follows a constant ratio like 12:30 = 2:5, and then map this ratio to the second pair 14:x. Step-by-Step Solution: Compute the ratio of the first pair: 12:30 can be simplified by dividing both numbers by 6, giving 2:5.Assuming the same ratio holds for 14 and the unknown number x, we set up 14:x = 2:5.From the property of proportions, x = (14 × 5) / 2.Calculate x: 14 × 5 = 70, and 70 ÷ 2 = 35. So the missing number must be 35. Verification / Alternative check: Check that the simplified ratio 14:35 again reduces to 2:5. Divide both numbers by 7 to obtain 2:5, which matches the ratio from the first pair.This confirms that the same proportional relationship holds for both pairs, so the analogy is consistent. Why Other Options Are Wrong: Option 36 would give the ratio 14:36, which simplifies to 7:18 and does not match 2:5.Option 28 gives 14:28 = 1:2, which again is different from 2:5.Option 42 gives 14:42 = 1:3, which clearly does not match the original ratio either. Common Pitfalls: A frequent mistake is to look for an additive pattern, for example noticing that 12 + 18 = 30 and then wrongly adding the same increment to 14, which would give 32 instead of any offered option.Ignoring the possibility of a proportional relationship can easily lead to incorrect guesses in analogy questions. Final Answer: Maintaining the ratio 2:5 between the two numbers in each pair, the correct completion of the analogy is 35.

Question 7

If Q means "add to", J means "multiply by", T means "subtract from" (treated as the minus operation) and K means "divide by", then what is the value of 30 K 2 Q 3 J 6 T 5?

Accepted Answer

Introduction / Context: This question again uses coded operations, where letters stand in for familiar arithmetic operations. You must decode the expression accurately and then apply the standard order of operations. The tricky part lies in interpreting the wording for T as subtraction and then carefully handling division, multiplication, addition and subtraction in the correct sequence. Given Data / Assumptions: Q means "add to" (so it is +). J means "multiply by" (so it is ×). T means "subtract from", which we treat as the minus sign − in the final expression. K means "divide by" (so it is ÷). Expression: 30 K 2 Q 3 J 6 T 5. Standard precedence applies after decoding: division and multiplication before addition and subtraction. Concept / Approach: First, rewrite the entire coded expression in terms of the real arithmetic symbols. Then, evaluate using operator precedence. It is generally convenient to work from left to right while respecting the fact that division and multiplication must be resolved before addition and subtraction. Step-by-Step Solution: Decode the expression: 30 K 2 Q 3 J 6 T 5 becomes 30 ÷ 2 + 3 × 6 − 5.Apply division and multiplication first: 30 ÷ 2 = 15 and 3 × 6 = 18.Now the expression simplifies to 15 + 18 − 5.Evaluate from left to right: 15 + 18 = 33, then 33 − 5 = 28. Verification / Alternative check: We can rewrite the decoded expression as (30 / 2) + (3 * 6) - 5 to visually separate the operations and confirm our arithmetic.Calculating again, we get 15 + 18 - 5 = 28, which matches our first computation, so the result is reliable. Why Other Options Are Wrong: 18 would correspond to stopping after computing 30 ÷ 2 = 15 and 3 × 6 = 18 and then taking only one of these partial results rather than combining them with subtraction.31 might come from incorrectly grouping as 30 ÷ (2 + 3) × 6 − 5 or from misinterpreting one of the coded operations.103 is far too large and would require treating K as multiplication or ignoring division completely, which conflicts with the definitions. Common Pitfalls: A frequent mistake is to misread "subtract from" as reversing the order of subtraction, which would lead to 5 − (30 ÷ 2 + 3 × 6) instead of 30 ÷ 2 + 3 × 6 − 5.Another pitfall is forgetting that division and multiplication must be resolved before performing the final addition and subtraction. Final Answer: After decoding and evaluating correctly, the value of the expression is 28.

Question 8

In a group consisting only of buffaloes and ducks, the total number of legs is 24 more than twice the total number of heads. Assuming each buffalo has 4 legs and each duck has 2 legs, how many buffaloes are there in the group?

Accepted Answer

Introduction / Context: This is a classic word problem involving animals, heads and legs, which translates into a pair of simultaneous equations. Such problems test your ability to convert a real-world description into algebraic expressions and then solve for the required quantities, in this case the number of buffaloes. Given Data / Assumptions: The group consists only of buffaloes and ducks. Each buffalo has 1 head and 4 legs. Each duck has 1 head and 2 legs. The total number of legs is 24 more than twice the total number of heads. Concept / Approach: Let the number of buffaloes be b and the number of ducks be d. The total number of heads is b + d. The total number of legs is 4b + 2d. The condition "legs are 24 more than twice the heads" becomes an equation linking these quantities. We then solve for b, which is the required answer. Step-by-Step Solution: Total heads = b + d.Total legs = 4b + 2d.Twice the number of heads is 2(b + d) = 2b + 2d.The condition says: total legs = twice heads + 24. So 4b + 2d = 2b + 2d + 24.Subtract 2b + 2d from both sides: 2b = 24, so b = 12. Verification / Alternative check: If b = 12, let us check the relationship for any value of d. Heads = 12 + d, twice heads = 2(12 + d) = 24 + 2d.Legs = 4b + 2d = 4(12) + 2d = 48 + 2d.Difference between legs and twice heads is (48 + 2d) − (24 + 2d) = 24, which matches the given condition regardless of how many ducks are present. Why Other Options Are Wrong: If b = 6, then the leg equation would become 4(6) + 2d = 2(6 + d) + 24, leading to 24 + 2d = 12 + 2d + 24, which simplifies to 24 = 36, a contradiction.Similarly, choosing 18 or 24 for b would not satisfy the derived algebraic condition 2b = 24, so they cannot be correct. Common Pitfalls: A common error is to misinterpret "24 more than twice the number of heads" and write 4b + 2d + 24 = 2(b + d) instead of 4b + 2d = 2(b + d) + 24.Another pitfall is to try random combinations of buffaloes and ducks without forming equations, which is inefficient and prone to mistakes. Final Answer: The group must contain 12 buffaloes to satisfy the given condition.

Question 9

In a cricket match, five batsmen P, Q, R, S and T together score an average of 36 runs. Batsman S scores 5 runs more than T; T scores 8 runs fewer than P; Q scores as many runs as S and T together; and Q and R together score 107 runs. How many runs …

Accepted Answer

Introduction / Context: This is a multi-step word problem involving averages and several linear relationships among the runs scored by five batsmen. It tests logical translation of language into algebra and then systematic equation solving to determine the specific score of T, one of the batsmen. Given Data / Assumptions: Batsmen: P, Q, R, S and T. The average score is 36 runs, so the total score is 5 × 36 = 180 runs. S scores 5 more than T, so S = T + 5. T scores 8 fewer than P, so T = P − 8, or P = T + 8. Q scores as many as S and T combined, so Q = S + T. Q and R together score 107 runs, so Q + R = 107. Concept / Approach: We express all players scores in terms of the single variable T and then use the total-sum condition to solve for T. This method eliminates the other variables one by one and ultimately leads to a simple linear equation in T, which is easy to solve. Step-by-Step Solution: From S = T + 5 and P = T + 8, the scores of P and S are expressed in terms of T.Q = S + T = (T + 5) + T = 2T + 5.From Q + R = 107, we get R = 107 − Q = 107 − (2T + 5) = 102 − 2T.Total runs: P + Q + R + S + T = 180. Substitute P, Q, R and S in terms of T: (T + 8) + (2T + 5) + (102 − 2T) + (T + 5) + T.Simplify: combine like terms to get 3T + 120 = 180, so 3T = 60 and T = 20. Verification / Alternative check: If T = 20, then S = 25, P = 28, Q = S + T = 45 and R = 107 − Q = 62.Check the total: P + Q + R + S + T = 28 + 45 + 62 + 25 + 20 = 180, which matches 5 × 36, so the data is consistent. Why Other Options Are Wrong: If T were 24, P would be 32, S 29, Q 53 and R 54, giving a total different from 180, so that option fails.Testing T = 28 or 29 similarly leads to totals that do not equal 180, so those values do not satisfy all the given conditions. Common Pitfalls: A common mistake is to misread "T scored 8 fewer than P" and write P = T − 8 instead of P = T + 8, which completely changes the equations.Another error is to forget that the average is over five batsmen, leading to a wrong total score and therefore wrong algebra. Final Answer: From the consistent system of equations, T must have scored 20 runs.

Question 10

Solve the simultaneous equations 3(2u + v) = 7uv and 3(u + 3v) = 11uv and choose the correct pair (u, v) from the following options.

Accepted Answer

Introduction / Context: This problem involves a pair of nonlinear simultaneous equations in two variables u and v. The equations contain products of u and v, so they are not purely linear. The question asks which of the given ordered pairs (u, v) satisfies both equations at the same time. This tests substitution skills and the ability to check candidate solutions efficiently. Given Data / Assumptions: Equation 1: 3(2u + v) = 7uv. Equation 2: 3(u + 3v) = 11uv. We must find (u, v) that satisfies both equations simultaneously. Options give several candidate pairs for (u, v). Concept / Approach: One method is to manipulate the two equations algebraically to isolate u in terms of v or vice versa. Another practical approach, given that specific candidate pairs are provided, is to test each pair directly in both equations. The correct answer must satisfy both equations exactly, not just approximately, so careful arithmetic is required. Step-by-Step Solution: Consider option B: u = 1, v = 3/2.Substitute into Equation 1: left side is 3(2u + v) = 3(2*1 + 3/2) = 3(2 + 1.5) = 3 × 3.5 = 10.5. Right side is 7uv = 7 × 1 × 3/2 = 10.5. So Equation 1 is satisfied.Now check Equation 2 with u = 1 and v = 3/2. Left side is 3(u + 3v) = 3(1 + 3*(3/2)) = 3(1 + 9/2) = 3(11/2) = 33/2.Right side is 11uv = 11 × 1 × 3/2 = 33/2. So Equation 2 is also satisfied. Therefore, option B works. Verification / Alternative check: Check option A: u = 1, v = 0. For Equation 1, left side is 3(2*1 + 0) = 6, right side is 7*1*0 = 0, so it fails immediately.Check option C: u = 0, v = 3/4. For Equation 1, left side is 3(0 + 3/4) = 9/4, right side is 7*0*3/4 = 0, so it fails.Check option D: u = 0, v = 1. Equation 1 again gives a nonzero left side and zero right side, so it is not a solution either. Why Other Options Are Wrong: Any pair with u = 0 makes the right-hand side of both equations equal to zero, while the left sides are clearly nonzero due to the terms 3(2u + v) and 3(u + 3v). Hence options C and D cannot work.Option A fails because it makes v = 0, again causing the product term 7uv and 11uv to vanish, which is inconsistent with the nonzero left-hand sides. Common Pitfalls: A common error is to check only one of the two equations and stop as soon as it matches, without verifying the second equation.Another pitfall is careless arithmetic with fractions, especially when converting between fractional and decimal forms, which can cause a correct candidate like (1, 3/2) to be rejected mistakenly. Final Answer: The only pair that satisfies both equations is u = 1, v = 3/2.

Question 11

Without using a calculator, find the approximate value of (49.001)^2 and choose the nearest option.

Accepted Answer

Introduction / Context: This question tests your ability to approximate the square of a number that is very close to an easy benchmark value. Estimation skills like this are important in many aptitude tests because they allow you to check the reasonableness of answers without doing long, exact calculations. Given Data / Assumptions: We need to approximate (49.001)^2. We are given only coarse options: 2500, 2400, 2600 and 2300. We may use algebraic identities and basic mental arithmetic. We are looking for the closest approximate value, not an exact decimal expansion. Concept / Approach: Notice that 49.001 is extremely close to 49, whose square is easy to compute exactly as 49^2 = 2401. We can use the identity (a + b)^2 = a^2 + 2ab + b^2 with a = 49 and b = 0.001. Because b is very small compared to a, the extra terms 2ab and b^2 will be small corrections to 2401, so the square of 49.001 will be a little more than 2401, and very close to 2400 in the context of the given options. Step-by-Step Solution: Compute the benchmark square: 49^2 = (50 − 1)^2 = 2500 − 100 + 1 = 2401.Write 49.001 as 49 + 0.001. Using (a + b)^2, we have (49 + 0.001)^2 = 49^2 + 2 × 49 × 0.001 + (0.001)^2.Calculate the correction term: 2 × 49 × 0.001 = 0.098.The last term (0.001)^2 = 0.000001 is negligible at this scale.So (49.001)^2 ≈ 2401 + 0.098 ≈ 2401.098, which is slightly larger than 2401. Verification / Alternative check: Compare 2401.098 to each option. It is extremely far from 2600 and 2300, and about 100 units away from 2500.It is only about 1 unit away from 2400, which makes 2400 the best approximation among the choices. Why Other Options Are Wrong: 2500 would correspond roughly to 50^2, but 49.001 is clearly smaller than 50, so its square cannot be as large as 2500.2600 is even farther and would require a much larger base number, so it is clearly too big.2300 is too small because even 48^2 is 2304, and our number is larger than 48, so its square must exceed 2304. Common Pitfalls: A common error is to round 49.001 up to 50 and then square, giving 2500, without recognizing that a one unit increase at this scale significantly changes the square.Another pitfall is to ignore that we only need an approximate answer and attempt an exact multiplication, which wastes time and can lead to mistakes. Final Answer: The square of 49.001 is slightly above 2401 and is best approximated by 2400 among the given options.

Question 12

What should come in place of the question mark in the following expression involving mixed fractions? 3 1/6 + 4 1/2 − 2 2/3 − 1 11/12 = ?

Accepted Answer

Introduction / Context: This question checks your ability to work with mixed fractions, converting them to improper fractions, finding a common denominator and simplifying the result back into a mixed fraction. Careful fraction arithmetic is very important in many competitive examinations and real-life calculations where quantities are not whole numbers. Given Data / Assumptions: Expression: 3 1/6 + 4 1/2 − 2 2/3 − 1 11/12. All numbers are positive mixed fractions and standard arithmetic rules apply. We must perform addition and subtraction accurately, expressing the result as a simplified mixed fraction. Concept / Approach: The usual strategy is to convert each mixed fraction into an improper fraction, then convert all fractions to a common denominator, perform the required additions and subtractions, and finally simplify the result. Using the least common multiple of the denominators keeps calculations manageable and reduces the amount of simplification needed at the end. Step-by-Step Solution: Convert each mixed fraction: 3 1/6 = (3×6 + 1)/6 = 19/6.4 1/2 = (4×2 + 1)/2 = 9/2.2 2/3 = (2×3 + 2)/3 = 8/3.1 11/12 = (1×12 + 11)/12 = 23/12.The denominators are 6, 2, 3 and 12. The least common multiple is 12.Rewrite each fraction with denominator 12: 19/6 = 38/12, 9/2 = 54/12, 8/3 = 32/12, and 23/12 stays 23/12.Now compute: (38/12 + 54/12) − (32/12 + 23/12) = 92/12 − 55/12 = 37/12.Write 37/12 as a mixed fraction: 37 ÷ 12 = 3 with remainder 1, so the result is 3 1/12. Verification / Alternative check: We can sum the positive fractions first: 3 1/6 + 4 1/2 ≈ 3.17 + 4.5 = 7.67 (approximately).Sum the negative fractions: 2 2/3 + 1 11/12 ≈ 2.67 + 1.92 = 4.59 (approximately).Difference is about 7.67 − 4.59 ≈ 3.08, which is close to 3 1/12 (about 3.0833). This rough check supports our exact calculation. Why Other Options Are Wrong: An answer around 1 7/12 or 1 5/12 is too small because the positive terms clearly outweigh the negative terms by more than 3 units.3 7/12 is larger than 3 1/12 by half a unit, and would require a numerator of 43 over 12, which does not match the correctly obtained 37 over 12. Common Pitfalls: Students often make mistakes when converting mixed fractions to improper fractions by miscalculating the numerator.Another pitfall is forgetting to convert all fractions to a common denominator before adding or subtracting, which produces inconsistent results. Final Answer: The correct simplified value of the expression is 3 1/12.

Question 13

A sum of Rs 1890 is to be distributed as 9 cash prizes to customers of a supermarket for their overall purchases. Each prize is Rs 30 less than the preceding one. What is the least value among these nine prizes?

Accepted Answer

Introduction / Context: This question is based on arithmetic progression, where we have a fixed number of terms, a constant difference between consecutive terms and a given total sum. The prizes form a decreasing arithmetic sequence since each prize is Rs 30 less than the previous one. We are asked to find the smallest prize amount, which is the last term of this sequence when arranged from highest to lowest. Given Data / Assumptions: Total prize money = Rs 1890. Number of prizes n = 9. Each prize is Rs 30 less than the preceding one, so the common difference in a decreasing sequence is −30. We can equivalently consider an increasing sequence with difference +30 from the least prize upwards. Concept / Approach: Let the least prize be L. Then the next prizes are L + 30, L + 60, and so on, up to L + 8 × 30. These 9 values form an arithmetic progression with first term L, common difference 30 and 9 terms. The sum of an arithmetic progression is given by S = n/2 × [2a + (n − 1)d], where a is the first term and d is the common difference. We plug in the known values and solve for L. Step-by-Step Solution: Write the nine prizes as: L, L + 30, L + 60, …, L + 8 × 30.Here, a = L, d = 30 and n = 9.Apply the sum formula: S = n/2 × [2a + (n − 1)d] = 9/2 × [2L + 8 × 30].We are given S = 1890, so 1890 = 9/2 × (2L + 240).Multiply both sides by 2 to clear the fraction: 3780 = 9(2L + 240).Divide both sides by 9: 420 = 2L + 240, so 2L = 180 and L = 90. Verification / Alternative check: If the least prize is Rs 90, the prizes are 90, 120, 150, 180, 210, 240, 270, 300 and 330.Sum these: pair them symmetrically (90 + 330) + (120 + 300) + (150 + 270) + (180 + 240) + 210 = 420 + 420 + 420 + 420 + 210 = 1890.This matches the given total, confirming that L = 90 is correct. Why Other Options Are Wrong: A least prize of 80 or 85 would produce a different total sum, not equal to 1890, when the 9-term arithmetic progression is summed.Similarly, 95 as the least prize would give an overall sum larger than 1890 due to every term being higher. Common Pitfalls: Some students mistakenly take the highest prize as the first term without converting carefully between increasing and decreasing sequences.Another pitfall is forgetting the factor n/2 in the sum formula and using S = n(2a + (n − 1)d), which gives an incorrect equation for L. Final Answer: The least of the nine prizes, and hence the smallest amount, is Rs 90.

Question 14

By how much is the value of the expression −4 − (−10) greater than the value of the expression −10 − (−4)?

Accepted Answer

Introduction / Context: This problem tests basic operations with negative numbers and the correct interpretation of subtraction of negative terms. It asks for the difference between two expressions, both involving subtraction of negative numbers, which is a typical area where sign errors can occur if you do not proceed carefully. Given Data / Assumptions: Expression 1: −4 − (−10). Expression 2: −10 − (−4). We are asked: "How much greater" is Expression 1 than Expression 2? Standard rules for integer arithmetic apply. Concept / Approach: The key idea is that subtracting a negative number is equivalent to adding its positive counterpart. So we need to simplify each expression separately, then subtract the second result from the first to see how much larger it is. This is a direct application of sign rules in addition and subtraction of integers. Step-by-Step Solution: Simplify Expression 1: −4 − (−10). Subtracting a negative is adding a positive, so −4 − (−10) = −4 + 10.Compute −4 + 10 = 6.Simplify Expression 2: −10 − (−4) = −10 + 4.Compute −10 + 4 = −6.Now find how much greater 6 is than −6: 6 − (−6) = 6 + 6 = 12. Verification / Alternative check: You can visualize the numbers on a number line: −6 is 6 units left of zero, and 6 is 6 units right of zero.The distance between −6 and 6 is 12 units, which matches the computed difference. Why Other Options Are Wrong: An answer of 10 or 6 usually arises from incorrectly treating only one of the subtractions of a negative as addition while leaving the other unchanged.An answer of 0 would imply that both expressions are equal, which they clearly are not, since one simplifies to 6 and the other to −6. Common Pitfalls: The most frequent mistake is to forget that "minus minus" becomes plus, leading to expressions like −4 − (−10) being incorrectly simplified as −4 − 10.Another pitfall is to compare 6 and −6 by simply subtracting in the wrong order, such as −6 − 6, which would give −12 instead of the required positive difference. Final Answer: The value of −4 − (−10) is 12 greater than the value of −10 − (−4), so the required difference is 12.

Question 15

Let the roots of the quadratic equation 2x^2 + 5x + 3 = 0 be r1 and r2. Which of the following quadratic equations has roots equal to the reciprocals 1/r1 and 1/r2?

Accepted Answer

Introduction / Context: This question examines your understanding of how the coefficients of a quadratic equation relate to its roots, and in particular, how to find the quadratic equation whose roots are the reciprocals of the roots of a given quadratic. It uses Vieta relations that connect sums and products of roots with the coefficients of the equation. Given Data / Assumptions: Original equation: 2x^2 + 5x + 3 = 0. Roots of this equation are r1 and r2 (not explicitly given). We need an equation whose roots are 1/r1 and 1/r2. Options propose candidate quadratic equations in standard form. Concept / Approach: For a quadratic ax^2 + bx + c = 0 with roots r1 and r2, Vieta relations state that r1 + r2 = −b/a and r1r2 = c/a. If we define new roots s1 = 1/r1 and s2 = 1/r2, then their sum and product are: s1 + s2 = (r1 + r2)/(r1r2) and s1s2 = 1/(r1r2). Once we know these, we can form the new quadratic equation as x^2 − (s1 + s2)x + s1s2 = 0 and clear denominators to match one of the options. Step-by-Step Solution: For 2x^2 + 5x + 3 = 0, we have a = 2, b = 5, c = 3.Sum of roots r1 + r2 = −b/a = −5/2.Product of roots r1r2 = c/a = 3/2.Now, s1 = 1/r1 and s2 = 1/r2. Then s1 + s2 = (r1 + r2)/(r1r2) = (−5/2) / (3/2) = −5/3.Also, s1s2 = 1/(r1r2) = 1 / (3/2) = 2/3.So the required quadratic with roots 1/r1 and 1/r2 is x^2 − (s1 + s2)x + s1s2 = x^2 − (−5/3)x + 2/3 = x^2 + (5/3)x + 2/3 = 0.Multiply through by 3 to clear denominators: 3x^2 + 5x + 2 = 0. Verification / Alternative check: We can quickly check that if r is a root of 2x^2 + 5x + 3 = 0, then x = 1/r should satisfy 3x^2 + 5x + 2 = 0.Substitute x = 1/r into 3x^2 + 5x + 2 and multiply by r^2 to get 3 + 5r + 2r^2, which is just the original polynomial 2r^2 + 5r + 3 written in a different order. Since 2r^2 + 5r + 3 = 0, this confirms that 3x^2 + 5x + 2 = 0 has roots 1/r1 and 1/r2. Why Other Options Are Wrong: The coefficients in options B and C do not match the required sum and product of reciprocal roots. Their corresponding sums and products of roots differ from −5/3 and 2/3.Option D, "None", is incorrect because we have explicitly derived 3x^2 + 5x + 2 = 0 as the correct equation. Common Pitfalls: Some students incorrectly reverse the coefficients as c x^2 + b x + a without using Vieta relations carefully, which can happen to match only in some special cases.Another pitfall is forgetting to clear denominators after writing the new quadratic, leading to fractional coefficients that may not match any option even when the logic is correct. Final Answer: The required quadratic equation whose roots are the reciprocals of the roots of 2x^2 + 5x + 3 = 0 is 3x^2 + 5x + 2 = 0, corresponding to option A.

Question 16

Find the last two digits of the number 2151^415.

Accepted Answer

Introduction / Context: This question involves modular arithmetic and cyclic patterns in the last digits of powers. Instead of computing the full value of 2151^415, which is enormous, we only need the last two digits. This is a typical number theory problem where understanding remainders and repeating patterns makes the work manageable. Given Data / Assumptions: We need the last two digits of 2151^415. The last two digits of a number are determined by its remainder when divided by 100. 2151 and 100 are relatively large, but modular arithmetic allows simplification. Concept / Approach: The last two digits of a number depend only on the last two digits of its base. Therefore, 2151^415 and 51^415 have the same last two digits. We then analyze the pattern of powers of 51 modulo 100. If this pattern repeats with a short cycle, we can reduce the exponent 415 modulo the cycle length and find the result with a few small computations. Step-by-Step Solution: Reduce the base modulo 100: 2151 ≡ 51 (mod 100). So we only need the last two digits of 51^415.Compute 51^1 mod 100: 51.Compute 51^2 = 51 × 51 = 2601, so 51^2 ≡ 2601 mod 100 ≡ 1 (mod 100).Thus, 51^2 ≡ 1 (mod 100). This means every even power of 51 is congruent to 1 modulo 100 and every odd power is congruent to 51 modulo 100.Since 415 is odd, we can write 415 = 2k + 1. Therefore, 51^415 = 51^(2k + 1) = (51^2)^k × 51 ≡ 1^k × 51 ≡ 51 (mod 100).Hence, the last two digits of 51^415, and therefore of 2151^415, are 51. Verification / Alternative check: We can verify the pattern further by checking 51^3 = 51 × 51^2. Since 51^2 ≡ 1 (mod 100), we have 51^3 ≡ 51 × 1 = 51 (mod 100), consistent with the odd-power rule.Similarly, 51^4 = (51^2)^2 ≡ 1^2 = 1 (mod 100), confirming the cycle of length 2 in the last two digits. Why Other Options Are Wrong: Any alternative last two digits like 81, 61 or 91 would require a different remainder pattern modulo 100, which contradicts the strong cycle 51, 01, 51, 01 already observed for consecutive powers of 51.Since we have a clear algebraic argument based on 51^2 ≡ 1 (mod 100), the options 81, 61 and 91 cannot be correct. Common Pitfalls: A common mistake is to look only at the last digit and assume a pattern based on modulo 10 instead of modulo 100. That fails when the question asks specifically for two last digits.Another pitfall is attempting to compute extremely large powers directly or with approximate calculators, which is unnecessary and error prone. Final Answer: The last two digits of 2151^415 are 51.

Question 17

Evaluate the expression 7 + 7 ÷ 7 + 7 × 7 + 7 − 7 ÷ 7 + 7 × 7 using the standard order of operations.

Accepted Answer

Introduction / Context: This expression uses the same number, 7, combined with addition, subtraction, multiplication and division. The purpose is to test your ability to apply the standard order of operations correctly, especially when the same number appears many times and it is easy to get lost in the calculation. Given Data / Assumptions: Expression: 7 + 7 ÷ 7 + 7 × 7 + 7 − 7 ÷ 7 + 7 × 7. We follow standard precedence: all divisions and multiplications from left to right, then additions and subtractions from left to right. No brackets are implied beyond this precedence order. Concept / Approach: The strategy is to identify and compute each multiplication and division first while keeping track of the resulting simplified terms. Once all such operations are completed, we add and subtract the remaining terms in order. Working step by step reduces the chance of confusion in long expressions with repeated numbers. Step-by-Step Solution: Start with the full expression: 7 + 7 ÷ 7 + 7 × 7 + 7 − 7 ÷ 7 + 7 × 7.Compute each division: 7 ÷ 7 = 1 and another 7 ÷ 7 = 1.Compute each multiplication: 7 × 7 = 49 and another 7 × 7 = 49.Now the expression becomes 7 + 1 + 49 + 7 − 1 + 49.Combine the terms from left to right: 7 + 1 = 8, 8 + 49 = 57, 57 + 7 = 64, 64 − 1 = 63, and 63 + 49 = 112. Verification / Alternative check: We can group similar terms to check: There are three plain 7 terms (7 + 7 + 7) giving 21.There are two division contributions (7 ÷ 7 + 7 ÷ 7) giving 1 + 1 = 2.There are two multiplication contributions (7 × 7 + 7 × 7) giving 49 + 49 = 98.Combine these: 21 + 2 + 98 − 1 (because one of the divisions is subtracted) actually already accounted as 7 − 7 ÷ 7, which we simplified in order, leading to the same total of 112. The step-by-step route is clearer and already shows this. Why Other Options Are Wrong: An answer of 56 or 98 usually comes from ignoring some of the terms or miscounting the multiplication contributions.A result of 0 would require extensive cancellation that does not actually occur in this expression, so it indicates a serious error in handling the operations. Common Pitfalls: Many students incorrectly evaluate from left to right without respecting the higher precedence of division and multiplication, leading to wrong results.Another pitfall is to miscopy or omit one of the repeated 7 terms, especially when the expression is long. Final Answer: Correctly applying the order of operations, the expression evaluates to 112.

Question 18

Using the standard order of operations, find the value of 3 × 3 + 3 − 3 + 3.

Accepted Answer

Introduction / Context: This is a straightforward arithmetic expression designed to check whether you correctly apply the order of operations in a situation where the same number, 3, appears several times. Even simple expressions can produce errors if multiplication is not carried out before addition and subtraction. Given Data / Assumptions: Expression: 3 × 3 + 3 − 3 + 3. We must apply standard precedence: multiplication first, then addition and subtraction from left to right. All numbers are integers and operations are exact. Concept / Approach: The only operation with higher precedence here is the multiplication 3 × 3. After computing this product, we are left with a sequence of additions and subtractions that can be evaluated from left to right. The key is to ensure that we do not treat all operations as if they have the same priority. Step-by-Step Solution: First perform the multiplication: 3 × 3 = 9.Substitute back into the expression to obtain 9 + 3 − 3 + 3.Now evaluate left to right: 9 + 3 = 12.Next, 12 − 3 = 9.Finally, 9 + 3 = 12. Verification / Alternative check: We can also group the terms: 3 × 3 + (3 − 3) + 3.Here, 3 × 3 = 9 and (3 − 3) = 0, so the expression becomes 9 + 0 + 3 = 12.This grouping again confirms the value 12. Why Other Options Are Wrong: An answer of 9 would result from stopping the evaluation at 3 × 3 or from miscalculating one of the addition or subtraction steps.An answer of 3 might come from grouping 3 × (3 + 3 − 3 + 3) incorrectly instead of respecting the original structure.A negative result such as −3 clearly conflicts with the fact that most terms are positive and the net effect is an increase in value. Common Pitfalls: One common mistake is to perform 3 + 3 first and then multiply by 3, which effectively changes the expression and leads to a different result.Another pitfall is to rush through the plus and minus operations and miscount them, for example, canceling the wrong pair of 3s. Final Answer: Correctly applying the order of operations, the value of the expression is 12.

Question 19

Find the value of 5068 ÷ 37 × 4 (use the standard order of operations and choose the closest integer option if needed).

Accepted Answer

Introduction / Context: This numerical question checks your ability to handle division followed by multiplication using the standard order of operations. Since the division does not yield an exact integer, it also tests your skill in approximating to the nearest reasonable integer option, which is a common requirement in aptitude tests. Given Data / Assumptions: Expression: 5068 ÷ 37 × 4. Division and multiplication have the same precedence and are evaluated from left to right. The answer choices are whole numbers, so an approximate integer value is expected. Concept / Approach: We first perform the division 5068 ÷ 37 to obtain a decimal value. Then we multiply this by 4. Because 37 is not a factor of 5068, the division does not simplify to a neat integer, so we round the result to the nearest whole number at an appropriate stage to match the answer choices. Working step by step prevents confusion between the operations. Step-by-Step Solution: Compute 5068 ÷ 37. This is approximately 137.027 (since 37 × 137 = 5069, which is very close to 5068).Now multiply the approximate quotient by 4: 137.027 × 4 ≈ 548.108.The closest integer to 548.108 is 548.Among the options given, 548 matches this approximate value and is therefore the best choice. Verification / Alternative check: Check 37 × 548 ÷ 4 to see how close we are to 5068. First compute 37 × 548 = 20276.Divide by 4: 20276 ÷ 4 = 5069, which differs from 5068 by only 1.This confirms that our earlier quotient estimate for 5068 ÷ 37 was very close to 137 and that 548 is a reasonable rounded result for the entire expression. Why Other Options Are Wrong: 625 would require the approximate value of 5068 ÷ 37 ÷ 4 or some other misordering of operations, and does not fit the left-to-right evaluation of the given expression.214 is far too small and suggests that either the division result was miscomputed or that the multiplication by 4 was omitted.745 is too large and would correspond to overestimating 5068 ÷ 37 significantly. Common Pitfalls: A common mistake is to rearrange the expression as 5068 ÷ (37 × 4), which gives a completely different and much smaller result.Another pitfall is to round the division too coarsely at an early stage, leading to a final approximation that does not match any option well. Final Answer: Evaluating 5068 ÷ 37 × 4 and rounding to the nearest integer, the value is best represented by 548.

Question 20

Using the conventional order of operations, compute the value of 7 + 7 ÷ 7 + 7 × 7 − 7.

Accepted Answer

Introduction / Context: This expression again uses the same number, 7, combined with different operations. The question is meant to reinforce the rule that division and multiplication must be executed before addition and subtraction, even when the numbers look symmetric and tempting to combine in other ways. Given Data / Assumptions: Expression: 7 + 7 ÷ 7 + 7 × 7 − 7. Standard precedence: perform division and multiplication before addition and subtraction. No hidden brackets are implied beyond this precedence. Concept / Approach: We first identify the division 7 ÷ 7 and the multiplication 7 × 7. Once these are simplified, we are left with a straightforward combination of additions and subtractions. Evaluating systematically from left to right after resolving multiplication and division ensures accuracy. Step-by-Step Solution: Start with 7 + 7 ÷ 7 + 7 × 7 − 7.Compute division: 7 ÷ 7 = 1.Compute multiplication: 7 × 7 = 49.Substitute back: the expression becomes 7 + 1 + 49 − 7.Now evaluate left to right: 7 + 1 = 8.Then 8 + 49 = 57.Finally, 57 − 7 = 50. Verification / Alternative check: We can group as (7 − 7) + (7 ÷ 7) + 7 × 7. Here, 7 − 7 = 0, 7 ÷ 7 = 1 and 7 × 7 = 49.Summing yields 0 + 1 + 49 = 50, which is identical to the previous result, confirming our calculation. Why Other Options Are Wrong: An answer of 42 might come from incorrectly evaluating 7 × 7 − 7 as 42 and ignoring the other terms or combining them incorrectly.A value like 57 would appear if the subtraction of 7 at the end is mistakenly omitted.Zero would require all terms to cancel out perfectly, which obviously does not happen in this expression. Common Pitfalls: Performing operations strictly from left to right without regard to precedence can lead learners to compute (7 + 7) ÷ 7, which changes the structure of the expression.Another pitfall is to misread the expression as 7(1 + 1 + 7 − 1), which is not equivalent to the given question and thus yields the wrong answer. Final Answer: Applying the correct order of operations, the expression evaluates to 50.

Mathematical Operations Questions