Mathematics and Quantitative Aptitude
What this domain tests
Number system, percentage, ratio and proportion, average, profit and loss, simple and compound interest, time and work, speed and distance, mensuration and elementary data interpretation. Most items are solvable in two steps if you convert the statement into one clean equation instead of calculating in your head.
Core rules
- Percentage change = (change ÷ original) × 100; divide by the base, never by the new value.
- Profit percentage is on cost price unless the question says "on marked price".
- SI = PRT/100; for two years, CI – SI = P(r/100)².
- Time and work: take the LCM of the given days as total work, then find each person's units per day.
- Trains: distance covered = length of train + length of platform when crossing a platform.
- Speed conversion: km/h × 5/18 = m/s.
Worked example
A finishes a work in 12 days and B in 18 days. How long do they take together? Take total work = LCM(12, 18) = 36 units. A does 36/12 = 3 units a day; B does 36/18 = 2 units a day; together 5 units a day. Time = 36 ÷ 5 = 7.2 days, that is 7⅕ days. Check by fractions: 1/12 + 1/18 = 3/36 + 2/36 = 5/36, so time = 36/5 days - the same answer.
Traps that cost marks
- Adding successive discounts: 20% then 10% is not 30%, it is 20 + 10 − 2 = 28%.
- Using selling price as the base for a profit percentage.
- Averaging two group averages without weighting by group size.
- Mixing metres with centimetres, or km/h with m/s, inside one calculation.