Percentages appear in almost every Quantitative Reasoning set. With about 40 seconds per question, the multiplier method is the fastest reliable approach.
Multipliers
- Increase by 20% → multiply by 1.20.
- Decrease by 20% → multiply by 0.80.
- Two changes in a row multiply: +10% then −10% is 1.10 × 0.90 = 0.99, a 1% fall overall.
Percentage change
Percentage change = (new − old) ÷ old × 100. Always divide by the original value. A price that goes from $80 to $100 rose by 25%, not 20%.
Reverse percentages
If a price after a 25% increase is $150, the original price is 150 ÷ 1.25 = $120. Taking 25% off $150 gives $112.50 — the classic wrong answer.
💡 Estimate before you calculate. If the answer must be a bit less than 150, any option above 150 is already out.