| 385 | a | ÷ | 5 | + | 270 | ( | 1 | − | a | ) | ÷ | 3 | = | 809 10 |
| 方程左边 = | 77 | a | + | 90 | ( | 1 | − | a | ) |
| 77 | a | + | 90 | ( | 1 | − | a | ) | = | 809 10 |
| 方程左边 = | 77 | a | + | 90 | × | 1 | − | 90 | a |
| = | 77 | a | + | 90 | − | 90 | a |
| = | - | 13 | a | + | 90 |
| - | 13 | a | + | 90 | = | 809 10 |
| - | 13 | a | = | 809 10 | − | 90 |
| - | 13 | a | = | - | 91 10 |
91 10 | = | 13 | a |
| 13 | a | = | 91 10 |
| a | = | 91 10 | ÷ | 13 |
| = | 91 10 | × | 1 13 |
| = | 7 10 | × | 1 |
| a | = | 7 10 |
| a | = | 0.7 |