Mathematics / Quantitative Aptitude
Domain 3 - Mathematics / Quantitative Aptitude
Number system, percentage, ratio–proportion, average, profit and loss, simple and compound interest, time–speed–distance, time and work, mensuration and data interpretation. Speed and accuracy matter more than advanced technique.
Core rules worth memorising
- Percentage change = (change ÷ original) × 100, always on the original value.
- Profit% and loss% are calculated on cost price unless stated otherwise.
- Successive discounts of a% and b% give a single discount of a + b − ab/100.
- Simple interest = PRT/100; compound amount = P(1 + R/100)^T.
- Work: if A does a job in x days and B in y days, together they take xy/(x + y) days.
- Speed conversion: km/h × 5/18 = m/s.
Worked example
An article bought for ₹480 is sold for ₹552. Find the profit per cent. Profit = 552 − 480 = ₹72. Profit% = 72/480 × 100 = 15%. Check with the shortcut: 552/480 = 1.15, so the sale price is 115% of cost, i.e. 15% profit.
Traps that cost marks
- Applying the percentage to the selling price instead of the cost price.
- Adding successive discounts directly (10% + 20% is not 30%, it is 28%).
- Forgetting unit conversion in time–speed questions - the commonest single error.
- In time and work, adding days instead of adding rates (1/x + 1/y).
- Rounding too early; keep fractions until the final step.
Practice discipline
Do 20 mixed questions in 20 minutes daily and log every wrong answer by topic, not by question.