| 2 | × | 40 | X | × | 30 | = | 2 | × | 120 | ( | 50 | − | X | ) | × | 20 |
| 方程左边 = | 2400 | X |
| 2400 | X | = | 2 | × | 120 | ( | 50 | − | X | ) | × | 20 |
| 方程右边 = | 4800 | ( | 50 | − | X | ) |
| 2400 | X | = | 4800 | ( | 50 | − | X | ) |
| 方程右边 = | 4800 | × | 50 | − | 4800 | X |
| = | 240000 | − | 4800 | X |
| 2400 | X | = | 240000 | − | 4800 | X |
| 2400 | X | + | 4800 | X | = | 240000 |
| 7200 | X | = | 240000 |
| X | = | 240000 | ÷ | 7200 |
| = | 240000 | × | 1 7200 |
| = | 100 | × | 1 3 |
| X | = | 100 3 |
| X | = | 33.333333 |