Mathematics / Quantitative Aptitude
What this domain tests
Numerical ability at senior-secondary level: simplification, percentage, ratio and proportion, average, profit and loss, simple and compound interest, time and work, speed and distance, mensuration and data interpretation.
Core rules
- Percentage change is always computed on the base named in the question.
- A discount is applied to the marked price; profit is computed on the cost price.
- For two years, CI minus SI equals P(r/100)².
- Time and work: take the LCM of the given days as total units, then add or subtract work rates.
- Trains: same direction subtract speeds, opposite direction add; distance is the train length, plus platform length while crossing.
- Average equals total divided by count; for unequal groups use the weighted average.
Worked example
A trader marks goods 40% above cost and allows a 25% discount. Find the profit percent. Reasoning: Let CP = 100. Marked price = 140. Selling price = 140 × 75/100 = 105. Profit = 5 on a cost of 100, so 5%. Note the sequence: mark-up on CP first, then discount on MP.
Traps that cost marks
- Subtracting percentages directly (40 − 25 = 15) instead of multiplying the factors.
- Using CP as the base for a discount.
- Applying the CI formula when the question says half-yearly or quarterly without adjusting r and n.
- Forgetting to convert km/h to m/s by multiplying by 5/18.
- In data interpretation, approximate only after checking how far apart the options are.