| 100 | ( | 1 | − | m% | ) | × | 30 | + | 200 | ( | 1 | + | 2 | × | m% | ) | ( | 20 | ( | 1 | − | m% | ) | ) | = | 7000 |
| 方程左边 = | 3000 | ( | 1 | − | m% | ) | + | 200 | ( | 1 | + | 2 | × | m% | ) | ( | 20 | ( | 1 | − | m% | ) | ) |
| 3000 | ( | 1 | − | m% | ) | + | 200 | ( | 1 | + | 2 | × | m% | ) | ( | 20 | ( | 1 | − | m% | ) | ) | = | 7000 |
| 方程左边 = | 3000 | × | 1 | − | 3000 | × | m% | + | 200 | ( | 1 | + | 2 | × | m% | ) | ( | 20 | ( | 1 | − | m% | ) | ) |
| = | 3000 | − | 30 | m | + | 200 | ( | 1 | + | 2 | × | m% | ) | ( | 20 | ( | 1 | − | m% | ) | ) |
| = | 3000 | − | 30 | m | + | 200 | × | 1 | ( | 20 | ( | 1 | − | m% | ) | ) | + | 200 | × | 2 | × | m% | ( | 20 | ( | 1 | − | m% | ) | ) |
| = | 3000 | − | 30 | m | + | 200 | ( | 20 | ( | 1 | − | m% | ) | ) | + | 4 | m | ( | 20 | ( | 1 | − | m% | ) | ) |
| = | 3000 | − | 30 | m | + | 200 | × | 20 | ( | 1 | − | m% | ) | + | 4 | m | ( | 20 | ( | 1 | − | m% | ) | ) |
| = | 3000 | − | 30 | m | + | 4000 | ( | 1 | − | m% | ) | + | 4 | m | ( | 20 | ( | 1 | − | m% | ) | ) |
| = | 3000 | − | 30 | m | + | 4000 | × | 1 | − | 4000 | × | m% | + | 4 | m | ( | 20 | ( | 1 | − | m% | ) | ) |
| = | 3000 | − | 30 | m | + | 4000 | − | 40 | m | + | 4 | m | ( | 20 | ( | 1 | − | m% | ) | ) |
| = | 7000 | − | 70 | m | + | 4 | m | ( | 20 | ( | 1 | − | m% | ) | ) |
| = | 7000 | − | 70 | m | + | 4 | m | × | 20 | ( | 1 | − | m% | ) |
| = | 7000 | − | 70 | m | + | 80 | m | ( | 1 | − | m% | ) |
| = | 7000 | − | 70 | m | + | 80 | m | × | 1 | − | 80 | m | × | m% |
| = | 7000 | − | 70 | m | + | 80 | m | − | 4 5 | m | m |
| = | 7000 | + | 10 | m | − | 4 5 | m | m |
| 7000 | + | 10 | m | − | 4 5 | m | m | = | 7000 |
| m2= | 25 2 |