| x | ( | 100 100 | + | 5 100 | ) | × | 80 100 | ( | 100 100 | − | 5 100 | ) | − | x | = | 7 |
| 方程左边 = | x | × | 100 100 | × | 80 100 | ( | 100 100 | − | 5 100 | ) | + | x | × | 5 100 | × | 80 100 | ( | 100 100 | − | 5 100 | ) | − | x |
| = | x | × | 4 5 | ( | 100 100 | − | 5 100 | ) | + | x | × | 1 25 | ( | 100 100 | − | 5 100 | ) | − | x |
| = | x | × | 4 5 | × | 100 100 | − | x | × | 4 5 | × | 5 100 | + | x | × | 1 25 | ( | 100 100 | − | 5 100 | ) | − | x |
| = | x | × | 4 5 | − | x | × | 1 25 | + | x | × | 1 25 | ( | 100 100 | − | 5 100 | ) | − | x |
| = | - | 6 25 | x | + | x | × | 1 25 | ( | 100 100 | − | 5 100 | ) |
| = | - | 6 25 | x | + | x | × | 1 25 | × | 100 100 | − | x | × | 1 25 | × | 5 100 |
| = | - | 6 25 | x | + | x | × | 1 25 | − | x | × | 1 500 |
| = | - | 101 500 | x |
| - | 101 500 | x | = | 7 |
| - | 7 | = | 101 500 | x |
101 500 | x | = | - | 7 |
| x | = | - | 7 | ÷ | 101 500 |
| = | - | 7 | × | 500 101 |
| x | = | - | 3500 101 |
| x | = | - 34.653465 |