| 2 | × | 120 | x | = | 3 | × | 100 | ( | 30 | − | x | ) |
| 方程左边 = | 240 | x |
| 240 | x | = | 3 | × | 100 | ( | 30 | − | x | ) |
| 方程右边 = | 300 | ( | 30 | − | x | ) |
| 240 | x | = | 300 | ( | 30 | − | x | ) |
| 方程右边 = | 300 | × | 30 | − | 300 | x |
| = | 9000 | − | 300 | x |
| 240 | x | = | 9000 | − | 300 | x |
| 240 | x | + | 300 | x | = | 9000 |
| 540 | x | = | 9000 |
| x | = | 9000 | ÷ | 540 |
| = | 9000 | × | 1 540 |
| = | 50 | × | 1 3 |
| x | = | 50 3 |
| x | = | 16.666667 |