| ( | 80000 | + | 75 | x | ) | ÷ | ( | 80000 | + | 100 | x | ) | = | 7 | ÷ | 8 |
| 方程两边同时乘以: | ( | 80000 | + | 100 | x | ) |
| ( | 80000 | + | 75 | x | ) | = | 7 | ÷ | 8 | × | ( | 80000 | + | 100 | x | ) |
| 80000 | + | 75 | x | = | 7 | ÷ | 8 | × | ( | 80000 | + | 100 | x | ) |
| 80000 | + | 75 | x | = | 7 | ÷ | 8 | × | 80000 | + | 7 | ÷ | 8 | × | 100 | x |
| 80000 | + | 75 | x | = | 70000 | + | 175 2 | x |
| 75 | x | − | 175 2 | x | = | 70000 | − | 80000 |
| - | 25 2 | x | = | 70000 | − | 80000 |
| - | 25 2 | x | = | - | 10000 |
| 10000 | = | 25 2 | x |
25 2 | x | = | 10000 |
| x | = | 10000 | ÷ | 25 2 |
| = | 10000 | × | 2 25 |
| = | 400 | × | 2 |
| x | = | 800 |