3.3 The Fraction-to-Percentage Conversion Table
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This table is the single highest-value piece of memorization in the entire quant syllabus. Once you know it cold, you can compute percentages of large numbers mentally in seconds instead of doing long multiplication. Every serious aspirant should be able to recite this table without hesitation.
| Fraction | Percentage | Fraction | Percentage |
|---|---|---|---|
| 1/2 | 50% | 1/11 | 9 1/11 % (9.09%) |
| 1/3 | 33 1/3 % (33.33%) | 1/12 | 8 1/3 % (8.33%) |
| 1/4 | 25% | 1/13 | 7 9/13 % (7.69%) |
| 1/5 | 20% | 1/14 | 7 1/7 % (7.14%) |
| 1/6 | 16 2/3 % (16.67%) | 1/15 | 6 2/3 % (6.67%) |
| 1/7 | 14 2/7 % (14.29%) | 1/16 | 6.25% |
| 1/8 | 12.5% | 1/17 | 5 15/17 % (5.88%) |
| 1/9 | 11 1/9 % (11.11%) | 1/18 | 5 5/9 % (5.56%) |
| 1/10 | 10% | 1/19 | 5 5/19 % (5.26%) |
| — | — | 1/20 | 5% |
Useful multiples worth memorizing alongside the table: 2/3 = 66.67%, 3/4 = 75%, 1/25 = 4%, 1/40 = 2.5%, 1/50 = 2%, 3/8 = 37.5%, 5/8 = 62.5%, 7/8 = 87.5%, 2/5 = 40%, 3/5 = 60%, 4/5 = 80%.
Once these are memorized, calculating “12.5% of 640” is not a multiplication problem — it’s a division problem: 12.5% = 1/8, so the answer is 640 ÷ 8 = 80, done in your head.
Notice a pattern in the table: as the denominator increases by 1, the percentage value decreases, and the amount of decrease itself shrinks (the gap between 1/2 and 1/3 is 16.67 percentage points, but the gap between 1/12 and 1/13 is only about 0.64 percentage points). This is simply because percentage values are inversely proportional to the denominator, and it explains why questions rarely test fractions beyond 1/20 — the percentage values become too close together to be useful as clean, distinguishable answer options in an MCQ. For any fraction 1/n where n is larger than 20, it is faster to estimate using nearby table values than to memorize further entries; for instance, 1/24 lies between 1/25 (4%) and 1/20 (5%), so a quick estimate of “just above 4%” is often precise enough to eliminate MCQ options without full calculation.