| ( | 50 | − | 40 | ) | × | 40 | × | 10 | + | 40 | x | = | 50 | x |
| Left side of the equation = | ( | 50 | − | 40 | ) | × | 400 | + | 40 | x |
| ( | 50 | − | 40 | ) | × | 400 | + | 40 | x | = | 50 | x |
| Left side of the equation = | 50 | × | 400 | − | 40 | × | 400 | + | 40 | x |
| = | 20000 | − | 16000 | + | 40 | x |
| = | 4000 | + | 40 | x |
| 4000 | + | 40 | x | = | 50 | x |
| 40 | x | − | 50 | x | = | - | 4000 |
| - | 10 | x | = | - | 4000 |
| 4000 | = | 10 | x |
| 10 | x | = | 4000 |
| x | = | 4000 | ÷ | 10 |
| = | 4000 | × | 1 10 |
| = | 400 | × | 1 |
| x | = | 400 |