Use the part-to-whole ratio as a cross-check
30:200 simplifies to 3:20. Reading that reduced ratio as a decimal and multiplying by 100 gives the same percentage, which is a useful check on the direct formula.
- 1.Form the ratio 30 ÷ 200.
- 2.30 ÷ 200 = 0.15.
- 3.0.15 × 100 = 15%.