| ( | 21 200 | − | 1 20 | ) | ÷ | ( | 3 20 | − | 1 20 | ) | = | ( | x | − | 50 | ) | ÷ | ( | 100 | − | 50 | ) |
| 方程两边同时乘以: | ( | 3 20 | − | 1 20 | ) | , | ( | 100 | − | 50 | ) |
| ( | 21 200 | − | 1 20 | ) | ( | 100 | − | 50 | ) | = | ( | x | − | 50 | ) | ( | 3 20 | − | 1 20 | ) |
21 200 | ( | 100 | − | 50 | ) | − | 1 20 | ( | 100 | − | 50 | ) | = | ( | x | − | 50 | ) | ( | 3 20 | − | 1 20 | ) |
21 200 | ( | 100 | − | 50 | ) | − | 1 20 | ( | 100 | − | 50 | ) | = | x | ( | 3 20 | − | 1 20 | ) | − | 50 | ( | 3 20 | − | 1 20 | ) |
21 200 | × | 100 | − | 21 200 | × | 50 | − | 1 20 | ( | 100 | − | 50 | ) | = | x | ( | 3 20 | − | 1 20 | ) | − | 50 | ( | 3 20 | − | 1 20 | ) |
21 200 | × | 100 | − | 21 200 | × | 50 | − | 1 20 | ( | 100 | − | 50 | ) | = | x | × | 3 20 | − | x | × | 1 20 | − | 50 | ( | 3 20 | − | 1 20 | ) |
21 2 | − | 21 4 | − | 1 20 | ( | 100 | − | 50 | ) | = | x | × | 3 20 | − | x | × | 1 20 | − | 50 | ( | 3 20 | − | 1 20 | ) |
21 4 | − | 1 20 | ( | 100 | − | 50 | ) | = | 1 10 | x | − | 50 | ( | 3 20 | − | 1 20 | ) |
21 4 | − | 1 20 | × | 100 | + | 1 20 | × | 50 | = | 1 10 | x | − | 50 | ( | 3 20 | − | 1 20 | ) |
21 4 | − | 1 20 | × | 100 | + | 1 20 | × | 50 | = | 1 10 | x | − | 50 | × | 3 20 | + | 50 | × | 1 20 |
21 4 | − | 5 | + | 5 2 | = | 1 10 | x | − | 15 2 | + | 5 2 |
11 4 | = | 1 10 | x | − | 5 |
| - | 1 10 | x | = | - | 5 | − | 11 4 |
| - | 1 10 | x | = | - | 31 4 |
31 4 | = | 1 10 | x |
1 10 | x | = | 31 4 |
| x | = | 31 4 | ÷ | 1 10 |
| = | 31 4 | × | 10 |
| = | 31 2 | × | 5 |
| x | = | 155 2 |
| x | = | 77.5 |