| 60 | × | 20 | = | ( | 60 | + | 20 | ) | ( | 20 | − | x | ) |
| 方程左边 = | 1200 |
| 1200 | = | ( | 60 | + | 20 | ) | ( | 20 | − | x | ) |
| 方程右边 = | 60 | ( | 20 | − | x | ) | + | 20 | ( | 20 | − | x | ) |
| = | 60 | × | 20 | − | 60 | x | + | 20 | ( | 20 | − | x | ) |
| = | 1200 | − | 60 | x | + | 20 | ( | 20 | − | x | ) |
| = | 1200 | − | 60 | x | + | 20 | × | 20 | − | 20 | x |
| = | 1200 | − | 60 | x | + | 400 | − | 20 | x |
| = | 1600 | − | 80 | x |
| 1200 | = | 1600 | − | 80 | x |
| 80 | x | = | 1600 | − | 1200 |
| 80 | x | = | 400 |
| x | = | 400 | ÷ | 80 |
| = | 400 | × | 1 80 |
| = | 5 | × | 1 |
| x | = | 5 |