The Case Math Playbook covers WHAT to calculate. This guide is about doing it fast. None of these tricks are clever for their own sake; each one replaces a slow, error-prone operation with a quick one you can do out loud without losing your train of thought.
The fraction-percent table (memorize this cold)
Division is slow; multiplying by a known percentage is fast. Every GMAT high-scorer and every consultant has this table memorized:
| Fraction | Percent | Fraction | Percent |
|---|---|---|---|
| 1/2 | 50% | 1/8 | 12.5% |
| 1/3 | 33.3% | 1/9 | 11.1% |
| 1/4 | 25% | 1/10 | 10% |
| 1/5 | 20% | 1/11 | 9.1% |
| 1/6 | 16.7% | 1/12 | 8.3% |
| 1/7 | 14.3% | 1/20 | 5% |
How it pays off: "divide $840M across 7 regions" becomes 840 × 14.3% ≈ $120M. "One competitor out of 12 exits, how much share is up for grabs?" is instantly ~8%. It works in reverse too: seeing "37%" should make you think "a bit over a third."
Create a free account to read the rest.
It takes a minute, and reading is always free.