Quantitative Aptitude / Numerical Ability
What this domain tests
Quantitative Aptitude / Numerical Ability checks arithmetic fluency and interpretation: simplification, number series, percentages, ratio, averages, time-work, time-speed-distance, interest, mixtures and data interpretation through tables, bar or line graphs and caselets. Speed matters, but accuracy is scored.
Core rules and concepts
- Convert common fractions to percentages: 1/8 = 12.5%, 1/6 = 16 2/3%, 1/12 = 8 1/3%.
- Profit and loss: fix CP = 100 when a problem gives only percentage changes; successive discounts multiply, they do not add.
- Simple vs compound interest: SI = P x R x T / 100; CI = P[(1 + R/100)^T - 1].
- Time and work: take total work as the LCM of individual days; combined rate is the sum of rates.
- DI: read units, axes and footnotes first; calculate only what the question asks.
Worked example
A trader marks an article 40% above cost and allows a 25% discount. Find profit percent. Let CP = 100. Marked price = 140. Discount = 25% of 140 = 35. SP = 140 - 35 = 105. Profit = 105 - 100 = 5. Profit% = 5/100 x 100 = 5%. Answer: 5%. Check: successive multipliers are 1.40 x 0.75 = 1.05, confirming 5%.
Traps
- Taking discount on CP instead of MP.
- Adding successive percentage changes instead of multiplying them.
- Mixing units in speed/time questions; 1 km/h = 5/18 m/s.
- Rounding in the middle of a DI calculation and then choosing a close but wrong option.
- Assuming every number series follows one operation; check differences, ratios and squares.
Key points
Use multipliers for percentage chains and LCM for work problems.