Numerical Reasoning and Quantitative Aptitude
What this section tests
Arithmetic fluency under time pressure: percentages, ratio and proportion, averages, profit and loss, discount, simple and compound interest, time–speed–distance, time and work, number series, LCM and HCF, and approximation.
Techniques
Convert percentages into multipliers. A 20% increase is ×1.2; a 10% decrease is ×0.9. Successive changes multiply - they never add. For averages, remember that total = average × count, which turns most average questions into simple equations. In ratio problems, introduce a multiplier k or fix a common unit so the parts become comparable. For number series, test differences first, then ratios, then squares and cubes, then alternating patterns.
Traps
- Percentage change is always computed on the stated base. A price rising from 80 to 100 has risen 25%, not 20%.
- Successive changes are not additive: +20% then −10% gives +8%, not +10%.
- Average speed over equal distances is the harmonic mean, not the arithmetic mean of the two speeds.
- Discount applies to the marked price; profit applies to the cost price.
- Unit mismatches: convert minutes to hours and grams to kilograms before computing.
Worked example
A salary rises 20% and then falls 10%. Use multipliers: 1.20 × 0.90 = 1.08, so the salary ends 8% above its starting value. Verify with a base of 100: 100 → 120 → 108. The common wrong answer, 10%, comes from adding the changes instead of multiplying them.
Rule of thumb
Estimate first, compute second, and check that the answer's direction and size are plausible.