Quantitative Aptitude: Multipliers and Bases
What to master
Quant covers arithmetic (percentage, ratio, average, profit–loss, SI/CI, time–speed–distance, time–work, mixtures), number system, mensuration and geometry, and data interpretation. Most CET questions are one or two steps, so formula recall and clean conversion matter more than exotic shortcuts.
Traps
- Percentage base. A 20% rise then a 20% fall leaves 96%, not 100%. Successive changes multiply; they never add.
- Average speed. Equal distances at 30 and 60 km/h average to 40 km/h (harmonic mean), not 45.
- Discounts. Two successive discounts of 20% and 10% total 28% off, since 0.8 × 0.9 = 0.72.
- Time and work. Convert days to rates (1/x per day) before adding; never average the days directly.
- Units and approximation. DI options are close - check whether the table is in lakh or crore, and whether the stem says "approximately".
- CI versus SI. Compound interest exceeds simple interest by the interest earned on the first year's interest.
Rule of thumb
For every successive-change problem, work with multipliers: +20% → 1.2, −20% → 0.8, then multiply and convert back.
Worked example
A shopkeeper marks an item 40% above cost and allows a 25% discount. Multiplier = 1.4 × 0.75 = 1.05, so the profit is 5% of cost. Candidates who subtract 40 − 25 = 15 confidently pick 15% and lose the mark.