Quantitative Aptitude and Numerical Ability
Quantitative Aptitude and Numerical Ability tests arithmetic speed and accuracy. Topics include percentages, ratio and proportion, averages, profit and loss, simple and compound interest, time-work, time-speed-distance, mensuration and data interpretation.
Core rules
- Percentage change = (change ÷ original) × 100; successive changes multiply, not add.
- Profit% is on cost price unless stated; discount% is on marked price.
- Simple interest = P × R × T ÷ 100; compound interest = P(1 + R/100)^T - P.
- Work rate is added for people working together; time = total work ÷ combined rate.
- Average speed for equal distances is harmonic: 2xy/(x+y), not (x+y)/2.
Worked example
A can finish a job in 12 days and B in 18 days. How long together? Take total work as LCM 36 units. A does 3 units/day and B does 2 units/day. Combined rate = 5 units/day. Time = 36 ÷ 5 = 7.2 days, or 7 days 4.8 hours. The LCM method avoids fractions and keeps the reasoning visible.
Traps
Convert minutes to hours before using speed formulas. Do not add successive percentage discounts; apply them one after another. In compound interest, the number of compounding periods matters. In ratio questions, ensure the totals refer to the same base. In data interpretation, read units (lakh, crore, thousand) before calculating.
Accuracy habit
Estimate the answer first, then compute. If the estimate and option differ by a factor of 10, check unit conversion.