| 360 | − | ( | 400 | − | x | ) | = | ( | 400 | − | x | ) | × | 20 100 |
| 方程左边 = | 360 | − | 400 | + | x |
| = | - | 40 | + | x |
| - | 40 | + | x | = | ( | 400 | − | x | ) | × | 20 100 |
| 方程右边 = | 400 | × | 20 100 | − | x | × | 20 100 |
| = | 80 | − | x | × | 20 100 |
| - | 40 | + | x | = | 80 | − | 20 100 | x |
| x | + | 20 100 | x | = | 80 | + | 40 |
6 5 | x | = | 80 | + | 40 |
6 5 | x | = | 120 |
| x | = | 120 | ÷ | 6 5 |
| = | 120 | × | 5 6 |
| = | 20 | × | 5 |
| x | = | 100 |