Quantitative Aptitude: shortcut-friendly arithmetic
The quantitative section is elementary mathematics with a speed requirement: percentages, ratio and proportion, averages, profit and loss, simple and compound interest, time–work, time–speed–distance, mensuration, number system, and data interpretation. Most questions are designed to be solved by a fraction or a ratio rather than full long multiplication.
Core rules
- Percentages: learn fraction equivalents (12.5% = 1/8, 16⅔% = 1/6, 20% = 1/5). Percentage change is always computed on the original base.
- Profit and loss: work on CP = 100. SP after successive changes is found by multiplying factors.
- Averages: total = average × count; combined average uses weighted totals.
- Time–work: convert to rates (1/n per day) and add rates, not times.
- Speed: 1 km/h = 5/18 m/s; in relative speed, add for opposite directions, subtract for same direction.
Worked example
A trader marks an item 40% above cost and then allows a 25% discount. Take CP = 100. Marked price = 140. After 25% discount, SP = 140 × 0.75 = 105, so the profit is 5%. The reasoning matters: multiply successive factors, never add 40 and subtract 25, which would wrongly give 15%.
Traps that cost marks
- Adding percentage changes instead of multiplying factors.
- Computing profit percentage on SP instead of CP.
- In compound interest, applying simple interest for the second year.
- In DI, reading the axis scale wrongly or mixing absolute values with percentages.