| ( | x | − | ( | - | 20 | ) | ) | × | 10 | × | 10 | = | 3000 |
| 方程左边 = | ( | x | − | ( | - | 20 | ) | ) | × | 100 |
| ( | x | − | ( | - | 20 | ) | ) | × | 100 | = | 3000 |
| 方程左边 = | x | × | 100 | − | ( | - | 20 | ) | × | 100 |
| = | 100 | x | + | 20 | × | 100 |
| = | 100 | x | + | 2000 |
| 100 | x | + | 2000 | = | 3000 |
| 100 | x | = | 3000 | − | 2000 |
| 100 | x | = | 1000 |
| x | = | 1000 | ÷ | 100 |
| = | 1000 | × | 1 100 |
| = | 10 | × | 1 |
| x | = | 10 |