| 3 | a | × | 1 | ÷ | 2 | + | 1 | × | 1 | ÷ | 2 | × | 2 | + | ( | a | + | 2 | ) | × | 2 | × | 1 | ÷ | 2 | = | 15 |
| 方程左边 = | 3 2 | a | + | 1 | + | ( | a | + | 2 | ) | × | 1 |
3 2 | a | + | 1 | + | ( | a | + | 2 | ) | × | 1 | = | 15 |
| 方程左边 = | 3 2 | a | + | 1 | + | a | × | 1 | + | 2 | × | 1 |
| = | 3 2 | a | + | 1 | + | a | × | 1 | + | 2 |
| = | 5 2 | a | + | 3 |
5 2 | a | + | 3 | = | 15 |
5 2 | a | = | 15 | − | 3 |
5 2 | a | = | 12 |
| a | = | 12 | ÷ | 5 2 |
| = | 12 | × | 2 5 |
| a | = | 24 5 |
| a | = | 4.8 |