| ( | 100 | + | X | ) | ÷ | ( | 100 | + | X | ÷ | 19 20 | ) | = | 19 20 |
| 方程两边同时乘以: | ( | 100 | + | X | ÷ | 19 20 | ) |
| ( | 100 | + | X | ) | = | 19 20 | ( | 100 | + | X | ÷ | 19 20 | ) |
| 100 | + | X | = | 19 20 | ( | 100 | + | X | ÷ | 19 20 | ) |
| 100 | + | X | = | 19 20 | × | 100 | + | 19 20 | X | ÷ | 19 20 |
| 100 | + | X | = | 95 | + | 1 | X |
| X | − | 1 | X | = | 95 | − | 100 |
| 0 | X | = | 95 | − | 100 |
| 0 | X | = | - | 5 |