Use the part-to-whole ratio as a cross-check
17:20 simplifies to 17:20. 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 17 ÷ 20.
- 2.17 ÷ 20 = 0.85.
- 3.0.85 × 100 = 85%.