| ( | x | − | 50 | ) | × | 3 4 | ÷ | 20 | = | ( | x | − | 20 | ) | × | 3 4 | ÷ | 40 |
| 方程左边 = | ( | x | − | 50 | ) | × | 3 80 |
| ( | x | − | 50 | ) | × | 3 80 | = | ( | x | − | 20 | ) | × | 3 4 | ÷ | 40 |
| 方程左边 = | x | × | 3 80 | − | 50 | × | 3 80 |
| = | x | × | 3 80 | − | 15 8 |
3 80 | x | − | 15 8 | = | ( | x | − | 20 | ) | × | 3 4 | ÷ | 40 |
| 方程右边 = | ( | x | − | 20 | ) | × | 3 160 |
3 80 | x | − | 15 8 | = | ( | x | − | 20 | ) | × | 3 160 |
| 方程右边 = | x | × | 3 160 | − | 20 | × | 3 160 |
| = | x | × | 3 160 | − | 3 8 |
3 80 | x | − | 15 8 | = | 3 160 | x | − | 3 8 |
3 80 | x | − | 3 160 | x | = | - | 3 8 | + | 15 8 |
3 160 | x | = | - | 3 8 | + | 15 8 |
3 160 | x | = | 3 2 |
| x | = | 3 2 | ÷ | 3 160 |
| = | 3 2 | × | 160 3 |
| = | 1 | × | 80 |
| x | = | 80 |