| 5 | − | 10 | x | − | 21 | ÷ | 5 | = | 3 | x | ÷ | 10 |
| 方程左边 = | 5 | − | 10 | x | − | 21 5 |
| = | 4 5 | − | 10 | x |
4 5 | − | 10 | x | = | 3 | x | ÷ | 10 |
| 方程右边 = | 3 10 | x |
4 5 | − | 10 | x | = | 3 10 | x |
| - | 10 | x | − | 3 10 | x | = | - | 4 5 |
| - | 103 10 | x | = | - | 4 5 |
4 5 | = | 103 10 | x |
103 10 | x | = | 4 5 |
| x | = | 4 5 | ÷ | 103 10 |
| = | 4 5 | × | 10 103 |
| = | 4 | × | 2 103 |
| x | = | 8 103 |
| x | = | 0.07767 |