| ( | a | × | 1 5 | + | a | ) | × | 1 5 | + | ( | a | × | 1 5 | ) | + | a | = | 171000 |
| 方程左边 = | a | × | 1 5 | × | 1 5 | + | a | × | 1 5 | + | ( | a | × | 1 5 | ) | + | a |
| = | a | × | 1 25 | + | a | × | 1 5 | + | ( | a | × | 1 5 | ) | + | a |
| = | 31 25 | a | + | ( | a | × | 1 5 | ) |
| = | 31 25 | a | + | a | × | 1 5 |
| = | 36 25 | a |
36 25 | a | = | 171000 |
| a | = | 171000 | ÷ | 36 25 |
| = | 171000 | × | 25 36 |
| = | 4750 | × | 25 |
| a | = | 118750 |