Quantitative Aptitude
Quantitative Aptitude
Numerical ability is tested through simplification and approximation, number series (including wrong-number series), quadratic comparison, data interpretation (table, bar, pie, line, caselet) and arithmetic word problems: percentage, ratio, average, time and work, speed and distance, simple and compound interest, profit and loss, mixtures, probability and mensuration. Data interpretation gives the most marks per question, while arithmetic supplies the accuracy that protects them.
Core rules
- Percentage change is always measured on the original base. Successive changes multiply: +20% then −20% is ×1.2 × 0.8 = 0.96, a net fall of 4%, not zero.
- Time and work: add rates, not days. Combined time = xy/(x+y).
- Average speed over equal distances = 2xy/(x+y); the plain mean of the speeds is always too high.
- Compound interest: A = P(1 + r/100)^t. For half-yearly compounding, halve the rate and double the time.
- Data interpretation: read the axis, units and the year asked before touching the options.
Worked example
A finishes a job in 12 days and B in 18 days. Working together, how long do they take?
Rates: A = 1/12 per day, B = 1/18 per day. Combined = 1/12 + 1/18 = 3/36 + 2/36 = 5/36 per day. Time = 36/5 = 7.2 days. The answer must be less than 12 days, so any option above 12 is eliminated before calculation.
Traps that cost marks
- Applying the simple-interest formula to a compound-interest question.
- Taking a percentage of the new value instead of the original.
- Mixing km/h and m/s (multiply by 5/18), or minutes and hours.
- In data interpretation, answering for the wrong year or ignoring the word "approximately".
- Rounding in the middle of a calculation instead of at the end.