Mathematics and Quantitative Aptitude
Mathematics and Quantitative Aptitude tests speed and accuracy in arithmetic, algebra, mensuration and data interpretation. Most questions are Class 8-10 level; the challenge is selecting the shortest method.
Core rules and concepts
- Percentage and profit/loss: profit% = (SP - CP)/CP x 100; discount is always on marked price.
- Ratio, average, mixture: alligation for two-component mixtures; weighted average when group sizes differ.
- Interest: SI = PRT/100; CI = P(1 + R/100)^T - P.
- Time-speed-distance: average speed = total distance/total time (not arithmetic mean of speeds).
- Time and work: use one-day work as a fraction; combine rates by addition.
- Mensuration: area and volume formulae; convert units before substituting.
Worked example
A shopkeeper marks an article 40% above cost and allows a 25% discount. Find profit%. Let CP = 100. Marked price = 140. Selling price = 140 x 0.75 = 105. Profit = 105 - 100 = 5, so profit% = 5%. The discount is applied to MP, not CP; applying 25% to CP would wrongly give a loss.
Traps that cost marks
Successive percentage changes are not additive: a 20% rise then 20% fall gives 96, not 100. In average speed, equal distances at different speeds require the harmonic mean. In CI, interest is added each period. Do not forget to convert minutes to hours in speed problems.