Quant Shortcuts for Banking Prelims: Percentages, Ratios and Simplification
Percentage–fraction pairs, a ratio check, and approximation for simplification, each with a worked example for IBPS and SBI prelims.
Banking prelims quant rewards a small set of conversions you can do without a pen stroke. Speed comes after the conversion is automatic. If a shortcut gives you a different answer from the long method on a practice item, drop the shortcut until you can see why.
Fractions you should not calculate
| Percent | Fraction | Use |
|---|---|---|
| 50% | 1/2 | Half of any base |
| 25% | 1/4 | Half of a half |
| 20% | 1/5 | Divide by 5 |
| 12.5% | 1/8 | Half of 25% |
| 10% | 1/10 | Move the decimal |
| 33⅓% | 1/3 | Do not write 0.33 unless the options are far apart |
Example. 12.5 percent of 640 is 640 divided by 8, which is 80. A successive change of +20 percent and then −20 percent is not zero. The net factor is 1.2 × 0.8 = 0.96, so the result is 4 percent less than the start. That net-factor step is worth more than a new formula.
Ratios and a digital check
If A:B is 3:5 and B:C is 2:3, give B a common multiple of 5 and 2, which is 10. Then A:B:C = 6:10:15. For simplification, a digital root can catch a wrong option. Add the digits of your result until one digit remains and compare with the option. It does not prove you are right. It only shows some answers are impossible. Approximation is for options that are far apart: round 49.7 to 50 only when the gap between options is larger than the error you just introduced.
Practice MCQs
1. 12.5% of 240 is: (a) 20 (b) 30 (c) 40 (d) 60
Answer: (b). 240/8 = 30.
2. A price rises 20% and then falls 20%. The net change is: (a) 0 (b) 4% decrease (c) 4% increase (d) 20% decrease
Answer: (b). 1.2 × 0.8 = 0.96.
3. If A:B = 2:3 and B:C = 3:4, then A:C is: (a) 2:3 (b) 3:4 (c) 1:2 (d) 3:2
Answer: (c). B is already 3 in both ratios, so A:B:C = 2:3:4 and A:C = 1:2.
4. 25% of a number is 80. The number is: (a) 160 (b) 240 (c) 320 (d) 400
Answer: (c). 80 × 4 = 320.
5. Approximation is safest when: (a) options differ by a wide margin (b) options differ by 0.01 (c) the question asks for an exact integer and options are adjacent (d) you have not read the question
Answer: (a).
Practice a quiz
The free practice set on the homepage needs no account. Use it after you read, while the facts are still fresh.
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