| ( | a | − | 80 | ) | ( | a | − | 120 | ) | ÷ | a | = | 24 | a | ÷ | 100 |
| 方程两边同时乘以: | a |
| ( | a | − | 80 | ) | ( | a | − | 120 | ) | = | 24 | a | ÷ | 100 | × | a |
| a | ( | a | − | 120 | ) | − | 80 | ( | a | − | 120 | ) | = | 24 | a | ÷ | 100 | × | a |
| a | ( | a | − | 120 | ) | − | 80 | ( | a | − | 120 | ) | = | 6 25 | a | a |
| a | a | − | a | × | 120 | − | 80 | ( | a | − | 120 | ) | = | 6 25 | a | a |
| a | a | − | 120 | a | − | 80 | a | + | 80 | × | 120 | = | 6 25 | a | a |
| a | a | − | 120 | a | − | 80 | a | + | 9600 | = | 6 25 | a | a |
| a | a | − | 200 | a | + | 9600 | = | 6 25 | a | a |