| ( | 130 | + | x | ) | ÷ | ( | 200 | + | x | ) | = | 7 10 |
| 方程两边同时乘以: | ( | 200 | + | x | ) |
| ( | 130 | + | x | ) | = | 7 10 | ( | 200 | + | x | ) |
| 130 | + | x | = | 7 10 | ( | 200 | + | x | ) |
| 130 | + | x | = | 7 10 | × | 200 | + | 7 10 | x |
| 130 | + | x | = | 140 | + | 7 10 | x |
| x | − | 7 10 | x | = | 140 | − | 130 |
3 10 | x | = | 140 | − | 130 |
3 10 | x | = | 10 |
| x | = | 10 | ÷ | 3 10 |
| = | 10 | × | 10 3 |
| x | = | 100 3 |
| x | = | 33.333333 |