| 20 | x | = | ( | 20 | + | 5 | ) | ( | x | − | 1 2 | ) |
| 方程右边 = | 20 | ( | x | − | 1 2 | ) | + | 5 | ( | x | − | 1 2 | ) |
| = | 20 | x | − | 20 | × | 1 2 | + | 5 | ( | x | − | 1 2 | ) |
| = | 20 | x | − | 10 | + | 5 | ( | x | − | 1 2 | ) |
| = | 20 | x | − | 10 | + | 5 | x | − | 5 | × | 1 2 |
| = | 20 | x | − | 10 | + | 5 | x | − | 5 2 |
| = | 25 | x | − | 25 2 |
| 20 | x | = | 25 | x | − | 25 2 |
| 20 | x | − | 25 | x | = | - | 25 2 |
| - | 5 | x | = | - | 25 2 |
25 2 | = | 5 | x |
| 5 | x | = | 25 2 |
| x | = | 25 2 | ÷ | 5 |
| = | 25 2 | × | 1 5 |
| = | 5 2 | × | 1 |
| x | = | 5 2 |
| x | = | 2.5 |