| 140 | × | 5 100 | ÷ | 140 | × | 100 | + | y | × | 9 100 | ÷ | y | × | 100 | = | 71 10 |
| 方程两边同时乘以: | y |
| 140 | × | 5 100 | ÷ | 140 | × | 100 | y | + | y | × | 9 100 | × | 100 | = | 71 10 | y |
| 140 | × | 5 100 | ÷ | 140 | × | 100 | y | + | y | × | 9 100 | × | 100 | − | 71 10 | y | = | 0 |
| 5 | y | + | y | × | 9 | − | 71 10 | y | = | 0 |
69 10 | y | = | 0 |
| y | = | 0 | ÷ | 69 10 |
| = | 0 | × | 10 69 |
| y | = | 0 |
| y | = | 0 |