| ( | 1 | − | 30 100 | ) | x | × | 7 | ÷ | 5 | − | 30 100 | x | = | 28 |
| 方程左边 = | ( | 1 | − | 30 100 | ) | x | × | 7 5 | − | 30 100 | x |
| ( | 1 | − | 30 100 | ) | x | × | 7 5 | − | 30 100 | x | = | 28 |
| 方程左边 = | 1 | x | × | 7 5 | − | 30 100 | x | × | 7 5 | − | 30 100 | x |
| = | 7 5 | x | − | 21 50 | x | − | 30 100 | x |
| = | 17 25 | x |
17 25 | x | = | 28 |
| x | = | 28 | ÷ | 17 25 |
| = | 28 | × | 25 17 |
| x | = | 700 17 |
| x | = | 41.176471 |