| 100 | ( | 1 | + | 10 100 | ) | ( | X | − | 400 | ) | = | 100 | X |
| 方程左边 = | 100 | × | 1 | ( | X | − | 400 | ) | + | 100 | × | 10 100 | ( | X | − | 400 | ) |
| = | 100 | ( | X | − | 400 | ) | + | 10 | ( | X | − | 400 | ) |
| = | 100 | X | − | 100 | × | 400 | + | 10 | ( | X | − | 400 | ) |
| = | 100 | X | − | 40000 | + | 10 | ( | X | − | 400 | ) |
| = | 100 | X | − | 40000 | + | 10 | X | − | 10 | × | 400 |
| = | 100 | X | − | 40000 | + | 10 | X | − | 4000 |
| = | 110 | X | − | 44000 |
| 110 | X | − | 44000 | = | 100 | X |
| 110 | X | − | 100 | X | = | 44000 |
| 10 | X | = | 44000 |
| X | = | 44000 | ÷ | 10 |
| = | 44000 | × | 1 10 |
| = | 4400 | × | 1 |
| X | = | 4400 |