Quantitative Aptitude / Numerical Ability
Quantitative Aptitude / Numerical Ability
This section tests arithmetic reasoning rather than advanced mathematics. Recurring areas are percentages, ratio and proportion, profit and loss, simple and compound interest, time–speed–distance, time and work, averages, number series, mensuration, and data interpretation from tables, bar charts and pie charts.
Core rules
- Percentage change is always calculated on the original base: change ÷ original × 100.
- Profit and loss: profit percentage is on cost price unless stated otherwise; discount is always on marked price.
- Successive changes do not simply add: changes of +20% and −20% give a net −4%, because 1.2 × 0.8 = 0.96.
- Interest: SI = PRT/100; CI = P(1 + R/100)^T − P.
- Time and work: convert days into rates. If A finishes in 12 days, A's one-day work is 1/12.
- Speed: distance = speed × time; convert km/h to m/s by multiplying by 5/18.
Worked example
A shopkeeper marks an article 40% above cost and then allows a 25% discount. What is his profit percentage? Let cost price = 100. Marked price = 140. Selling price = 140 × (1 − 0.25) = 105. Profit = 105 − 100 = 5, so profit = 5%.
Traps that cost marks
- Applying the discount to cost price instead of marked price.
- Using the new value as the base for a second percentage change.
- Mixing units (minutes with hours, metres with kilometres) in speed questions.
- In number series, stopping at first differences when the pattern is in the second differences.
- In data interpretation, reading the wrong year or axis, and ignoring the word "approximately".