| 40 | ( | 150 | ( | 1 | − | 10 100 | ) | ) | + | 20 | ( | 225 | ( | 1 | − | a% | ) | ) | = | 2000 |
| 方程左边 = | 40 | × | 150 | ( | 1 | − | 10 100 | ) | + | 20 | ( | 225 | ( | 1 | − | a% | ) | ) |
| = | 6000 | ( | 1 | − | 10 100 | ) | + | 20 | ( | 225 | ( | 1 | − | a% | ) | ) |
| = | 6000 | × | 1 | − | 6000 | × | 10 100 | + | 20 | ( | 225 | ( | 1 | − | a% | ) | ) |
| = | 6000 | − | 600 | + | 20 | ( | 225 | ( | 1 | − | a% | ) | ) |
| = | 5400 | + | 20 | ( | 225 | ( | 1 | − | a% | ) | ) |
| = | 5400 | + | 20 | × | 225 | ( | 1 | − | a% | ) |
| = | 5400 | + | 4500 | ( | 1 | − | a% | ) |
| = | 5400 | + | 4500 | × | 1 | − | 4500 | × | a% |
| = | 5400 | + | 4500 | − | 45 | a |
| = | 9900 | − | 45 | a |
| 9900 | − | 45 | a | = | 2000 |
| - | 45 | a | = | 2000 | − | 9900 |
| - | 45 | a | = | - | 7900 |
| 7900 | = | 45 | a |
| 45 | a | = | 7900 |
| a | = | 7900 | ÷ | 45 |
| = | 7900 | × | 1 45 |
| = | 1580 | × | 1 9 |
| a | = | 1580 9 |
| a | = | 175.555556 |