How do you quickly approximate a value like '3,487 is what percent of 15,012?' in a timed data interpretation section?
Round both numbers to friendly values close to the originals: 3,500 / 15,000 = 7/30, about 23.3%. The exact value is 23.23%, so the estimate is enough to pick the right option when choices are reasonably far apart.
Explain it simply
In a timed DI section you rarely need exact division. Round numbers so the ratio becomes a simple fraction, and know your fraction-to-percent table (1/3 = 33.3%, 1/6 = 16.7%, 1/8 = 12.5%, 1/7 = 14.3%). Round both numbers in the same direction to keep the error small, and switch to exact working only when options are close together.
Example
Question: 3,487 is what percent of 15,012? Options: (a) 19.6% (b) 23.2% (c) 26.4% (d) 31.1%.
- Round: 3,487 is close to 3,500; 15,012 is close to 15,000.
- 3,500 / 15,000 = 7/30 = 0.2333, about 23.3%.
- Only option (b), 23.2%, is near. Answer: (b).
Exact check: 3,487 / 15,012 = 0.23228..., which is 23.23%.
Another trick: 10% of 15,012 is about 1,500, so 20% is about 3,000. The remaining 487 is roughly 3.2% (since 1% is about 150). Total about 23.2%.
console.log(((3487 / 15012) * 100).toFixed(2)); // Output: 23.23
console.log(((3500 / 15000) * 100).toFixed(2)); // Output: 23.33What to say in the interview
"I round to 3,500 over 15,000, which is 7/30 or about 23.3%, and pick the nearest option. If two options were within half a percent, I'd do one more precise step, for example building it up from 10% and 1% chunks."
Common mistakes
- Rounding one number up and the other down, which doubles the error.
- Approximating when the options are very close together.