| X | = | 1400 | − | 1400 | ÷ | ( | 1 | + | 2 5 | ) |
| 方程两边同时乘以: | ( | 1 | + | 2 5 | ) |
| X | ( | 1 | + | 2 5 | ) | = | 1400 | ( | 1 | + | 2 5 | ) | − | 1400 |
| X | × | 1 | + | X | × | 2 5 | = | 1400 | ( | 1 | + | 2 5 | ) | − | 1400 |
| X | × | 1 | + | X | × | 2 5 | = | 1400 | × | 1 | + | 1400 | × | 2 5 | − | 1400 |
| X | × | 1 | + | X | × | 2 5 | = | 1400 | + | 560 | − | 1400 |
7 5 | X | = | 560 |
| X | = | 560 | ÷ | 7 5 |
| = | 560 | × | 5 7 |
| = | 80 | × | 5 |
| X | = | 400 |