| ( | 10 | + | x | ÷ | 5 | ) | ( | 800 | − | 20 | x | ) | = | 12000 |
| 方程左边 = | 10 | ( | 800 | − | 20 | x | ) | + | x | ÷ | 5 | × | ( | 800 | − | 20 | x | ) |
| = | 10 | × | 800 | − | 10 | × | 20 | x | + | x | × | 1 5 | ( | 800 | − | 20 | x | ) |
| = | 8000 | − | 200 | x | + | x | × | 1 5 | ( | 800 | − | 20 | x | ) |
| = | 8000 | − | 200 | x | + | x | × | 1 5 | × | 800 | − | x | × | 1 5 | × | 20 | x |
| = | 8000 | − | 200 | x | + | x | × | 160 | − | x | × | 4 | x |
| = | 8000 | − | 40 | x | − | x | × | 4 | x |
| 8000 | − | 40 | x | − | x | × | 4 | x | = | 12000 |