| x | × | 1 2 | × | 3 20 | × | 200 | = | 200 | x | × | 1 2 | − | 5 | x | − | 8000 |
| 方程左边 = | x | × | 15 |
| 15 | x | = | 200 | x | × | 1 2 | − | 5 | x | − | 8000 |
| 方程右边 = | 100 | x | − | 5 | x | − | 8000 |
| = | 95 | x | − | 8000 |
| 15 | x | = | 95 | x | − | 8000 |
| 15 | x | − | 95 | x | = | - | 8000 |
| - | 80 | x | = | - | 8000 |
| 8000 | = | 80 | x |
| 80 | x | = | 8000 |
| x | = | 8000 | ÷ | 80 |
| = | 8000 | × | 1 80 |
| = | 100 | × | 1 |
| x | = | 100 |