Quantitative Ability MCQs with Explanations

40% of 420 = 0.40 x 420 = 168, so 420 is the number. The tempting 336 is simply 168 x 2, which would be 80% of the answer, not 40% of it; 400 would give 160 at 40%.

Take cost = 100, so marked price = 140 and a 10% discount leaves selling price = 126, giving a profit of 26%. The 30% choice is the classic error of subtracting 10 from 40, but the discount is charged on the marked price, not on cost.

Simple interest = 12,000 x 10 x 2 / 100 = 2,400. Compound amount = 12,000 x 1.1 x 1.1 = 14,520, so compound interest = 2,520. The difference is 2,520 - 2,400 = 120.

The total needed for five innings is 42 x 5 = 210. He already has 34 + 46 + 28 + 52 = 160, so he must score 210 - 160 = 50.

Perimeter = 2(5x + 3x) = 16x = 240, so x = 15, giving length 75 m and breadth 45 m. Area = 75 x 45 = 3,375 sq m. The 3,600 option comes from wrongly treating 240 as the area input or rounding the sides to 60 and 60.

90 km/h = 90 x 5/18 = 25 m/s. The distance to be covered is the train plus the platform = 150 + 250 = 400 m, so time = 400 / 25 = 16 seconds. The 6 s and 10 s choices divide only the train length or only the platform length by 25.

Their one-day work adds to 1/10 + 1/15 = 3/30 + 2/30 = 5/30 = 1/6, so together they need 6 days. Averaging the two times (12.5 days) or adding them (25 days) are the standard traps: rates add, durations never do.

The gaps are 4, 6, 8, 10, rising by 2 each time, so the next gap is 12 and 30 + 12 = 42. The same terms are n(n+1): 1x2, 2x3, 3x4, 4x5, 5x6, then 6x7 = 42. Choosing 36 assumes the gap repeats at 6.

12 = 2^2 x 3, 18 = 2 x 3^2 and 30 = 2 x 3 x 5. The LCM takes the greatest powers, 2^2 x 3^2 x 5 = 180, while the HCF takes the common primes at their lowest powers, 2 x 3 = 6. The 60 and 90 options cannot be the LCM at all because neither is divisible by 12.

As decimals these are 3/7 = 0.4286, 5/11 = 0.4545, 7/13 = 0.5385 and 9/16 = 0.5625, so 9/16 is the largest. The tempting 7/13 is close behind at 0.538 but still smaller.

Square root of 0.16 is 0.4 because 0.4 x 0.4 = 0.16, and the cube root of 0.729 is 0.9 because 0.9 x 0.9 x 0.9 = 0.729. The sum is 0.4 + 0.9 = 1.3. The 1.1 option results from taking the cube root as 0.7.

Let the present ages be F and S. Then F - 10 = 4(S - 10) and F + 10 = 2(S + 10), which gives F = 2S + 10. Substituting: 2S + 10 - 10 = 4S - 40, so 2S = 40 and S = 20, making the father 50.

The mixture holds 4 litres of water and 36 litres of milk. Adding x litres of water requires (4 + x) / (40 + x) = 25/100 = 1/4, so 16 + 4x = 40 + x and 3x = 24, giving x = 8. Check: 48 litres containing 12 litres of water is exactly 25%.

There are 36 equally likely ordered outcomes and exactly four give a sum of 9: (3,6), (4,5), (5,4) and (6,3). So the probability is 4/36 = 1/9. The 5/36 option counts a fifth pair that does not exist.