Mathematics and Quantitative Aptitude: Speed with Structure
Concepts that recur
Quantitative aptitude tests arithmetic reasoning more than advanced maths. Prioritise percentages and profit-loss, ratio and proportion, time-speed-distance, time and work, averages, simple and compound interest, and mensuration. Learn the fraction-percentage table (1/8 = 12.5%, 1/6 ≈ 16.67%) to convert quickly.
Traps to expect
- Percentage change is calculated on the original value, not the new one.
- In successive discounts, never add them; use the formula a + b − ab/100.
- In time and work, convert days to rates (1/n per day) before adding.
- In compound interest, the number of compounding periods must match the rate period.
Worked example
A shopkeeper marks an item 40% above cost and gives a 25% discount. What is the profit percent? Let cost = 100. Marked price = 140. Selling price = 140 × 0.75 = 105. Profit = 5%. This shows why a headline discount can shrink a large markup.
Rule of thumb
For two successive changes of x% and y%, net change = x + y + xy/100 (with signs for increase/decrease). Practise 15 questions daily under a timer to build accuracy before speed.