Quantitative Aptitude
What the section tests
Quantitative Aptitude checks arithmetic fundamentals and calculation speed - percentage, ratio and proportion, average, profit and loss, simple and compound interest, time–speed–distance, time and work, mensuration, number system, and data interpretation from tables, bar graphs and pie charts.
Rules that carry most questions
- Percentage: every percentage needs a base; a change of a% followed by b% equals a + b + ab/100.
- Profit and loss: profit% is calculated on cost price unless stated otherwise; discount is always on marked price.
- CI vs SI: CI = P(1 + r/100)^n; SI = PRT/100; the two-year difference is P(r/100)².
- Time and work: work rate = 1/days; rates add; two workers together take xy/(x+y) days.
- Speed: km/h to m/s multiply by 5/18; average speed over equal distances is 2xy/(x+y), not (x+y)/2.
- Mensuration: cylinder volume πr²h, curved surface 2πrh, sphere 4/3πr³.
Worked example
A trader marks goods 40% above cost and allows a 25% discount. Find the profit percentage. Take CP = 100 → MP = 140 → SP = 140 × 0.75 = 105 → profit = 5 on 100 = 5%. Shortcut check: +40 then −25 gives 40 − 25 + (40 × −25)/100 = 15 − 10 = 5%.
Traps
- Subtracting 25 from 40 and answering 15% - the discount is charged on marked price, not cost.
- Applying a discount percentage to cost price instead of marked price.
- Averaging two speeds arithmetically when the distances are equal.
- "A is 25% more than B" means B is 20% less than A, not 25% less.
- Ignoring units (lakh vs crore) and the footnote under a pie chart.