Quantitative Aptitude and Numerical Ability
What this domain tests
Quantitative Aptitude tests speed and accuracy in arithmetic, number system, percentages, ratio and proportion, averages, time-work, speed-distance, interest, mensuration and data interpretation. Most questions are direct but designed to punish unit and percentage errors.
Core rules
- Percentage change = (change ÷ original) × 100; successive percentage changes are not additive.
- Ratio: convert all quantities to the same unit before forming the ratio.
- Time and work: use rates; if A finishes in x days, A’s one-day work is 1/x.
- Speed: 1 km/h = 5/18 m/s; average speed for equal distances is the harmonic mean, not the arithmetic mean.
- Interest: SI = PRT/100; CI = P(1 + R/100)^T − P.
Worked example
A marked price of ₹1,000 gets two successive discounts of 20% and 10%. After 20%, price = 800. After 10%, price = 800 × 0.9 = 720. Total discount = 280, so the net discount is 28%, not 30%. A single 30% discount would give 700, which is ₹20 lower.
Traps
Do not add successive percentages. Distinguish percentage points from percent change. In time-work, adding days instead of rates is wrong. In mensuration, keep all dimensions in the same unit. In data interpretation, read the axis scale and the year labels carefully.
Exam focus
Memorise fraction-to-percentage equivalents, squares to 30 and common mensuration formulas. Use approximation only after checking the options’ spacing.