Quantitative Aptitude: Arithmetic and Data Interpretation
Quantitative Aptitude checks speed and accuracy across simplification/approximation, number series, quadratic comparison, arithmetic (percentage, ratio, average, profit-loss, SI/CI, time-work, speed, mixture) and data interpretation.
Core rules
- Percentage change is always calculated on the base value; successive changes of a% and b% give a + b + ab/100.
- SI = PRT/100; CI = P[(1 + R/100)^T − 1]. For 2 years the CI–SI gap is P(R/100)².
- Work: combined one-day work is the sum of individual rates; time = 1 ÷ sum.
- In DI, read the units and the base (percentage of total vs percentage-point change) before calculating.
Worked example
Find the compound interest on ₹8,000 at 10% per annum for 2 years, compounded annually. Amount = 8,000 × (1.10)² = 8,000 × 1.21 = ₹9,680. CI = 9,680 − 8,000 = ₹1,680. Check with the shortcut: SI = 8,000 × 10 × 2/100 = ₹1,600; gap = 8,000 × (0.10)² = ₹80; CI = 1,600 + 80 = ₹1,680.
Traps
- Using SI when the question says compounded.
- Mixing metres and centimetres in mensuration, or minutes and hours in speed.
- Comparing percentages from different bases (profit on cost vs on selling price).
- Over-rounding in approximation questions where options are close.
- In number series, assuming a single difference pattern instead of checking ×, ÷ and square patterns.