| X | + | 400 | − | 3 | ÷ | 100 | × | ( | 20000 | + | X | ÷ | 13 100 | ) | = | 1800 |
| 方程左边 = | X | + | 400 | − | 3 100 | ( | 20000 | + | X | ÷ | 13 100 | ) |
| X | + | 400 | − | 3 100 | ( | 20000 | + | X | ÷ | 13 100 | ) | = | 1800 |
| 方程左边 = | X | + | 400 | − | 3 100 | × | 20000 | − | 3 100 | X | ÷ | 13 100 |
| = | X | + | 400 | − | 600 | − | 3 13 | X |
| = | 10 13 | X | − | 200 |
10 13 | X | − | 200 | = | 1800 |
10 13 | X | = | 1800 | + | 200 |
10 13 | X | = | 2000 |
| X | = | 2000 | ÷ | 10 13 |
| = | 2000 | × | 13 10 |
| = | 200 | × | 13 |
| X | = | 2600 |