| X | + | 20 | = | 5 | ÷ | 7 | × | ( | 3 | X | − | 20 | ) |
| 方程右边 = | 5 7 | ( | 3 | X | − | 20 | ) |
| X | + | 20 | = | 5 7 | ( | 3 | X | − | 20 | ) |
| 方程右边 = | 5 7 | × | 3 | X | − | 5 7 | × | 20 |
| = | 15 7 | X | − | 100 7 |
| X | + | 20 | = | 15 7 | X | − | 100 7 |
| X | − | 15 7 | X | = | - | 100 7 | − | 20 |
| - | 8 7 | X | = | - | 100 7 | − | 20 |
| - | 8 7 | X | = | - | 240 7 |
240 7 | = | 8 7 | X |
8 7 | X | = | 240 7 |
| X | = | 240 7 | ÷ | 8 7 |
| = | 240 7 | × | 7 8 |
| = | 30 | × | 1 |
| X | = | 30 |