| ( | 12 | − | X | ) | ÷ | 15 | + | ( | 5 | − | X | ) | ÷ | 10 | = | X | ÷ | 20 |
| 方程左边 = | 12 | × | 1 15 | − | X | × | 1 15 | + | ( | 5 | − | X | ) | × | 1 10 |
| = | 4 5 | − | X | × | 1 15 | + | ( | 5 | − | X | ) | × | 1 10 |
| = | 4 5 | − | 1 15 | X | + | 5 | × | 1 10 | − | X | × | 1 10 |
| = | 4 5 | − | 1 15 | X | + | 1 2 | − | X | × | 1 10 |
| = | 13 10 | − | 1 6 | X |
13 10 | − | 1 6 | X | = | X | ÷ | 20 |
| - | 1 6 | X | − | 1 20 | X | = | - | 13 10 |
| - | 13 60 | X | = | - | 13 10 |
13 10 | = | 13 60 | X |
13 60 | X | = | 13 10 |
| X | = | 13 10 | ÷ | 13 60 |
| = | 13 10 | × | 60 13 |
| = | 1 | × | 6 |
| X | = | 6 |