| 99 | × | 1 10 | = | 1 20 | ( | X | + | 1 10 | ) |
| 方程左边 = | 99 10 |
99 10 | = | 1 20 | ( | X | + | 1 10 | ) |
| 方程右边 = | 1 20 | X | + | 1 20 | × | 1 10 |
| = | 1 20 | X | + | 1 200 |
99 10 | = | 1 20 | X | + | 1 200 |
| - | 1 20 | X | = | 1 200 | − | 99 10 |
| - | 1 20 | X | = | - | 1979 200 |
1979 200 | = | 1 20 | X |
1 20 | X | = | 1979 200 |
| X | = | 1979 200 | ÷ | 1 20 |
| = | 1979 200 | × | 20 |
| = | 1979 10 | × | 1 |
| X | = | 1979 10 |
| X | = | 197.9 |