Numerical Reasoning
Numerical reasoning checks arithmetic fluency under time pressure: percentages, ratios, rates, averages, and number sequences, often framed in project or technology contexts. Accuracy matters, but so does judging whether an answer is plausible.
Core rules
- Percentage change: multiply by (1 ± r). A 25% rise followed by a 20% fall is 1.25 × 0.80 = 1.00, a net change of zero.
- Ratios: if A:B = 3:5 and A = 240, one part is 80, so the total is 8 parts = 640.
- Rates: distance = speed × time; work = rate × time; add rates when tasks run together.
- Averages: total = mean × count; weighted means weight by group size.
- Series: check differences, ratios, alternating rules, squares, and cubes.
Worked example: a sensor streams at 200 MB/s for 45 s, then at 150 MB/s for 30 s. First phase: 200 × 45 = 9,000 MB. Second: 150 × 30 = 4,500 MB. Total = 13,500 MB = 13.5 GB using 1 GB = 1,000 MB.
Traps that cost marks
- Adding successive percentages instead of multiplying.
- Mixing percent with percentage points.
- Using mismatched units, such as seconds with minutes.
- Averaging two averages without accounting for group sizes.
- Forgetting that 1 GB may mean 1,000 MB or 1,024 MB; use the convention stated.