| 20 | ÷ | ( | 200 | + | X | ) | = | 18 | ÷ | ( | 120 | + | X | ) |
| 方程两边同时乘以: | ( | 200 | + | X | ) | , | ( | 120 | + | X | ) |
| 20 | ( | 120 | + | X | ) | = | 18 | ( | 200 | + | X | ) |
| 20 | × | 120 | + | 20 | X | = | 18 | ( | 200 | + | X | ) |
| 20 | × | 120 | + | 20 | X | = | 18 | × | 200 | + | 18 | X |
| 2400 | + | 20 | X | = | 3600 | + | 18 | X |
| 20 | X | − | 18 | X | = | 3600 | − | 2400 |
| 2 | X | = | 3600 | − | 2400 |
| 2 | X | = | 1200 |
| X | = | 1200 | ÷ | 2 |
| = | 1200 | × | 1 2 |
| = | 600 | × | 1 |
| X | = | 600 |