| ( | P | + | 9 20 | ) | × | 500 | − | 1250 | = | 4000 | − | 250 | P |
| 方程左边 = | P | × | 500 | + | 9 20 | × | 500 | − | 1250 |
| = | P | × | 500 | + | 225 | − | 1250 |
| = | 500 | P | − | 1025 |
| 500 | P | − | 1025 | = | 4000 | − | 250 | P |
| 500 | P | + | 250 | P | = | 4000 | + | 1025 |
| 750 | P | = | 4000 | + | 1025 |
| 750 | P | = | 5025 |
| P | = | 5025 | ÷ | 750 |
| = | 5025 | × | 1 750 |
| = | 67 | × | 1 10 |
| P | = | 67 10 |
| P | = | 6.7 |