Mathematics / Quantitative Aptitude
Mathematics and Quantitative Aptitude is the highest-scoring section for a prepared candidate because the syllabus is finite: number system, simplification, HCF–LCM, percentage, ratio and proportion, average, profit and loss, simple and compound interest, time–work, time–speed–distance, mensuration and elementary data interpretation.
Formulas worth memorising
- Successive change: net % = a + b + ab/100, using negative signs for discounts.
- Profit% = (SP − CP)/CP × 100; it is computed on cost price unless stated otherwise.
- CI − SI for 2 years = P(r/100)²; for 3 years = P(r/100)²(3 + r/100).
- Work: if A finishes in x days and B in y days, together they take xy/(x + y) days.
- Average speed over equal distances = 2xy/(x + y).
Worked example
A trader marks an item 40% above cost and then allows a 25% discount. Find his profit percentage. Let CP = 100. Marked price = 140. Selling price = 140 × 0.75 = 105. Profit = 5 on a cost of 100, so 5%. The tempting answer 40 − 25 = 15 is wrong because the mark-up and the discount are calculated on different bases.
Traps that cost marks
- Applying a percentage change to the wrong base (CP versus MP versus SP).
- Reading "profit% on selling price" when the question means cost price.
- Unit mismatch - metres with centimetres, minutes with hours.
- Rounding in the middle of a calculation; carry fractions to the final step.
- In ratio questions, forgetting to convert parts to actual values before adding or subtracting.