| 200 | ( | 3 20 | − | x | ) | = | 100 | ( | x | − | 3 20 | ) |
| 方程左边 = | 200 | × | 3 20 | − | 200 | x |
| = | 30 | − | 200 | x |
| 30 | − | 200 | x | = | 100 | ( | x | − | 3 20 | ) |
| 方程右边 = | 100 | x | − | 100 | × | 3 20 |
| = | 100 | x | − | 15 |
| 30 | − | 200 | x | = | 100 | x | − | 15 |
| - | 200 | x | − | 100 | x | = | - | 15 | − | 30 |
| - | 300 | x | = | - | 15 | − | 30 |
| - | 300 | x | = | - | 45 |
| 45 | = | 300 | x |
| 300 | x | = | 45 |
| x | = | 45 | ÷ | 300 |
| = | 45 | × | 1 300 |
| = | 3 | × | 1 20 |
| x | = | 3 20 |
| x | = | 0.15 |