| ( | 94 | − | x | ) | ÷ | ( | 90 | − | x | ) | × | 100 | = | 120 |
| 方程两边同时乘以: | ( | 90 | − | x | ) |
| ( | 94 | − | x | ) | × | 100 | = | 120 | ( | 90 | − | x | ) |
| 94 | × | 100 | − | x | × | 100 | = | 120 | ( | 90 | − | x | ) |
| 94 | × | 100 | − | x | × | 100 | = | 120 | × | 90 | − | 120 | x |
| 9400 | − | x | × | 100 | = | 10800 | − | 120 | x |
| - | 100 | x | + | 120 | x | = | 10800 | − | 9400 |
| 20 | x | = | 10800 | − | 9400 |
| 20 | x | = | 1400 |
| x | = | 1400 | ÷ | 20 |
| = | 1400 | × | 1 20 |
| = | 70 | × | 1 |
| x | = | 70 |