| 85 | − | ( | - | 1 100 | ( | 1500 | − | x | ) | + | 100 | ) | = | 80 | − | ( | - | 1 100 | ( | 1000 | + | x | ) | + | 100 | ) |
| 方程左边 = | 85 | + | 1 100 | ( | 1500 | − | x | ) | − | 100 |
| = | - | 15 | + | 1 100 | ( | 1500 | − | x | ) |
| = | - | 15 | + | 1 100 | × | 1500 | − | 1 100 | x |
| = | - | 15 | + | 15 | − | 1 100 | x |
| = | - | 0 | − | 1 100 | x |
| - | 1 100 | x | = | 80 | − | ( | - | 1 100 | ( | 1000 | + | x | ) | + | 100 | ) |
| 方程右边 = | 80 | + | 1 100 | ( | 1000 | + | x | ) | − | 100 |
| = | - | 20 | + | 1 100 | ( | 1000 | + | x | ) |
| = | - | 20 | + | 1 100 | × | 1000 | + | 1 100 | x |
| = | - | 20 | + | 10 | + | 1 100 | x |
| = | - | 10 | + | 1 100 | x |
| - | 1 100 | x | = | - | 10 | + | 1 100 | x |
| - | 1 100 | x | − | 1 100 | x | = | - | 10 |
| - | 1 50 | x | = | - | 10 |
| 10 | = | 1 50 | x |
1 50 | x | = | 10 |
| x | = | 10 | ÷ | 1 50 |
| = | 10 | × | 50 |
| x | = | 500 |