Quantitative Reasoning
What you must know
This domain includes number series, numeric analogies (2 : 8 as 3 : ?), and short word problems. For series, test operations in a fixed order: constant difference, constant ratio, alternating operations, differences that themselves form a pattern, and familiar sequences (squares, primes, powers of two). For numeric analogies, identify the operation linking the first pair and apply the identical operation to the second term. For word problems, translate the words into an equation before computing, and track units - minutes against hours, cents against dollars.
Traps
- Series that switch operation mid-stream (add 3, multiply by 2, add 3...).
- Distractors built from one correct step of a two-step problem.
- Using the wrong base for a percentage increase or decrease.
- "How many more than" confused with "how many times as many."
- Off-by-one counting in inclusive ranges and fencepost problems.
Rule of thumb
Write the first differences beneath the series. If they are constant, stop there. If not, take the differences of the differences. Most items resolve within two levels or reveal an alternating pattern.
Worked example: 2, 6, 12, 20, 30, ? The differences are 4, 6, 8, 10, increasing by 2 each time, so the next difference is 12 and the answer is 42. The same result comes from the pattern n(n+1): 6 × 7 = 42.