Quantitative Techniques and Data Interpretation
Quantitative Techniques and Data Interpretation
This CMAT section (20 questions) is arithmetic-led: percentages, ratio and proportion, averages, profit and loss, simple and compound interest, time-speed-distance, time and work, mixtures, plus basic mensuration and counting. Roughly half the questions are pure computation; the rest are Data Interpretation sets - tables, bar/line/pie charts and caselets - where you must read the figure accurately and then apply a shortcut.
Rules worth memorising
- Successive percentage changes: net = a + b + ab/100. A 20% rise then a 20% fall is a net 4% fall, not zero.
- Profit and loss is computed on cost price unless stated; discount is always on marked price.
- For a constant distance, time is inversely proportional to speed; average speed over equal distances is 2xy/(x+y), never (x+y)/2.
- Compound interest: A = P(1 + r/100)^n; for two years, CI − SI = P(r/100)².
- In pie charts, convert angles to values first (1% = 3.6°).
Worked example
A trader marks goods 40% above cost, then allows successive discounts of 10% and 5%. Take CP = ₹100, so MP = ₹140. After 10%: ₹126. After 5%: ₹119.70, a net profit of 19.7%. Shortcut: two discounts of 10% and 5% combine to 10 + 5 − 0.5 = 14.5%, and 140 × 0.855 = 119.7. The common error is applying both discounts to cost price, or adding them into a flat 15%.
Traps
- Percentage points versus percent change in DI: a share moving from 20% to 25% is a 25% relative rise, not 5%.
- Averaging two group averages without weighting by group size.
- Unit mismatches: minutes versus hours, lakh versus crore, thousands.
- With a −1 penalty, unverified guessing across five options is a losing strategy; eliminate first.