| ( | 440 | + | m | ) | ÷ | 40 | = | ( | 310 | + | m | ) | ÷ | 30 |
| 方程左边 = | 440 | × | 1 40 | + | m | × | 1 40 |
| = | 11 | + | m | × | 1 40 |
| 11 | + | 1 40 | m | = | ( | 310 | + | m | ) | ÷ | 30 |
| 方程右边 = | 310 | × | 1 30 | + | m | × | 1 30 |
| = | 31 3 | + | m | × | 1 30 |
| 11 | + | 1 40 | m | = | 31 3 | + | 1 30 | m |
1 40 | m | − | 1 30 | m | = | 31 3 | − | 11 |
| - | 1 120 | m | = | 31 3 | − | 11 |
| - | 1 120 | m | = | - | 2 3 |
2 3 | = | 1 120 | m |
1 120 | m | = | 2 3 |
| m | = | 2 3 | ÷ | 1 120 |
| = | 2 3 | × | 120 |
| = | 2 | × | 40 |
| m | = | 80 |