| 80 | ÷ | x | = | ( | 200 | − | 80 | ) | ÷ | ( | x | + | 30 | ) |
| 方程两边同时乘以: | x | , | ( | x | + | 30 | ) |
| 80 | ( | x | + | 30 | ) | = | ( | 200 | − | 80 | ) | x |
| 80 | x | + | 80 | × | 30 | = | ( | 200 | − | 80 | ) | x |
| 80 | x | + | 80 | × | 30 | = | 200 | x | − | 80 | x |
| 80 | x | + | 2400 | = | 200 | x | − | 80 | x |
| 80 | x | + | 2400 | = | 120 | x |
| 80 | x | − | 120 | x | = | - | 2400 |
| - | 40 | x | = | - | 2400 |
| 2400 | = | 40 | x |
| 40 | x | = | 2400 |
| x | = | 2400 | ÷ | 40 |
| = | 2400 | × | 1 40 |
| = | 60 | × | 1 |
| x | = | 60 |