Quantitative Aptitude / Numerical Ability
Quantitative Aptitude / Numerical Ability tests whether you can choose the right method and compute cleanly under time pressure. The paper commonly draws on simplification and approximation, number series, percentage, ratio, average, profit and loss, simple and compound interest, time–work, speed–distance, mixtures and data interpretation.
Core rules
- Percentage change is calculated on the original base. A 20% rise followed by a 20% fall leaves 96% of the original, not 100%.
- Profit and loss: profit% and loss% are on cost price unless stated; discount is on marked price.
- Simple interest: SI = P × R × T / 100. Compound interest: A = P(1 + R/100)^T; CI = A − P.
- Time and work: take total work as the LCM of the days, or use rate = 1/days.
- Speed: convert km/h to m/s by multiplying by 5/18.
Worked example
A trader marks an article 40% above cost and allows a 25% discount. Let cost = ₹100. Marked price = ₹140. Selling price = 75% of 140 = ₹105. Profit = ₹5 on ₹100, so profit = 5%. The common mistake is taking 25% of cost instead of marked price.
Traps
Mixing cost price and marked price; applying successive percentages additively; using the wrong base in ratio–percentage conversion; forgetting unit conversion in speed questions; and approximating before checking whether the options are close together. In data interpretation, read the axis label and the year before calculating.