| ( | 631 | + | a | ) | ÷ | ( | 1107 | + | a | ) | = | 3 5 |
| 方程两边同时乘以: | ( | 1107 | + | a | ) |
| ( | 631 | + | a | ) | = | 3 5 | ( | 1107 | + | a | ) |
| 631 | + | a | = | 3 5 | ( | 1107 | + | a | ) |
| 631 | + | a | = | 3 5 | × | 1107 | + | 3 5 | a |
| 631 | + | a | = | 3321 5 | + | 3 5 | a |
| a | − | 3 5 | a | = | 3321 5 | − | 631 |
2 5 | a | = | 3321 5 | − | 631 |
2 5 | a | = | 166 5 |
| a | = | 166 5 | ÷ | 2 5 |
| = | 166 5 | × | 5 2 |
| = | 83 | × | 1 |
| a | = | 83 |