| 20 | × | 80 100 | x | + | 15 | ( | 100 | − | x | ) | × | 40 100 | = | 1000 |
| 方程左边 = | 16 | x | + | 6 | ( | 100 | − | x | ) |
| 16 | x | + | 6 | ( | 100 | − | x | ) | = | 1000 |
| 方程左边 = | 16 | x | + | 6 | × | 100 | − | 6 | x |
| = | 16 | x | + | 600 | − | 6 | x |
| = | 10 | x | + | 600 |
| 10 | x | + | 600 | = | 1000 |
| 10 | x | = | 1000 | − | 600 |
| 10 | x | = | 400 |
| x | = | 400 | ÷ | 10 |
| = | 400 | × | 1 10 |
| = | 40 | × | 1 |
| x | = | 40 |