| 400 | ( | 1 | − | x% | ) | ( | 1 | − | x% | ) | = | 324 |
| 方程左边 = | 400 | × | 1 | ( | 1 | − | x% | ) | − | 400 | × | x% | ( | 1 | − | x% | ) |
| = | 400 | ( | 1 | − | x% | ) | − | 4 | x | ( | 1 | − | x% | ) |
| = | 400 | × | 1 | − | 400 | × | x% | − | 4 | x | ( | 1 | − | x% | ) |
| = | 400 | − | 4 | x | − | 4 | x | ( | 1 | − | x% | ) |
| = | 400 | − | 4 | x | − | 4 | x | × | 1 | + | 4 | x | × | x% |
| = | 400 | − | 4 | x | − | 4 | x | + | 1 25 | x | x |
| = | 400 | − | 8 | x | + | 1 25 | x | x |
| 400 | − | 8 | x | + | 1 25 | x | x | = | 324 |