| ( | X | − | 640 | ) | ( | 1 | − | 40 100 | ) | ÷ | 240 | = | ( | X | − | 400 | ) | ( | 1 | − | 40 100 | ) | ÷ | 320 |
| 方程左边 = | X | ( | 1 | − | 40 100 | ) | × | 1 240 | − | 640 | ( | 1 | − | 40 100 | ) | × | 1 240 |
| = | X | ( | 1 | − | 40 100 | ) | × | 1 240 | − | 8 3 | ( | 1 | − | 40 100 | ) |
| = | X | × | 1 | × | 1 240 | − | X | × | 40 100 | × | 1 240 | − | 8 3 | ( | 1 | − | 40 100 | ) |
| = | X | × | 1 240 | − | X | × | 1 600 | − | 8 3 | ( | 1 | − | 40 100 | ) |
| = | 1 400 | X | − | 8 3 | ( | 1 | − | 40 100 | ) |
| = | 1 400 | X | − | 8 3 | × | 1 | + | 8 3 | × | 40 100 |
| = | 1 400 | X | − | 8 3 | + | 16 15 |
| = | 1 400 | X | − | 8 5 |
1 400 | X | − | 8 5 | = | ( | X | − | 400 | ) | ( | 1 | − | 40 100 | ) | ÷ | 320 |
| 方程右边 = | X | ( | 1 | − | 40 100 | ) | × | 1 320 | − | 400 | ( | 1 | − | 40 100 | ) | × | 1 320 |
| = | X | ( | 1 | − | 40 100 | ) | × | 1 320 | − | 5 4 | ( | 1 | − | 40 100 | ) |
| = | X | × | 1 | × | 1 320 | − | X | × | 40 100 | × | 1 320 | − | 5 4 | ( | 1 | − | 40 100 | ) |
| = | X | × | 1 320 | − | X | × | 1 800 | − | 5 4 | ( | 1 | − | 40 100 | ) |
| = | 3 1600 | X | − | 5 4 | ( | 1 | − | 40 100 | ) |
| = | 3 1600 | X | − | 5 4 | × | 1 | + | 5 4 | × | 40 100 |
| = | 3 1600 | X | − | 5 4 | + | 1 2 |
| = | 3 1600 | X | − | 3 4 |
1 400 | X | − | 8 5 | = | 3 1600 | X | − | 3 4 |
1 400 | X | − | 3 1600 | X | = | - | 3 4 | + | 8 5 |
1 1600 | X | = | - | 3 4 | + | 8 5 |
1 1600 | X | = | 17 20 |
| X | = | 17 20 | ÷ | 1 1600 |
| = | 17 20 | × | 1600 |
| = | 17 | × | 80 |
| X | = | 1360 |