Mathematics (Quantitative Aptitude)
Quantitative Aptitude tests school-level arithmetic under time pressure: number system, percentage, ratio and proportion, average, profit and loss, simple and compound interest, time-speed-distance, time and work, mensuration and data interpretation.
Core rules
- A rise of x% followed by a fall of x% gives a net fall of x²/100, never zero.
- Profit percentage is always calculated on cost price; discount is always calculated on marked price.
- Two successive discounts of a% and b% equal a + b − ab/100 as a single discount.
- SI = PRT/100; CI = P(1 + R/100)^T − P.
- In time and work, take the LCM of the given days as total work in units, then find each worker's units per day.
- For trains, relative speed adds when moving opposite and subtracts when moving in the same direction.
Worked example
A trader marks goods 40% above cost and allows 25% discount. Find the profit percentage. Reasoning: let CP = 100, so MP = 140. Discount is on MP, so SP = 140 × 0.75 = 105. Profit = 105 − 100 = 5 on a cost of 100, i.e. 5%. Note that naively adding 40% and subtracting 25% gives 15%, which is wrong because the discount applies to the marked price, not the cost price.
Traps
- Applying discount on CP instead of MP.
- Using the SI formula for a CI question, or forgetting to subtract P from the compounded amount.
- Mixing km/h with m/s; convert by multiplying by 5/18.
- Averaging averages of unequal groups without weighting them.
- Ignoring the "approximately" wording when options are far apart.