| ( | 4 | + | 1 10 | x | ) | ( | 500 | − | 10 | x | ) | = | 800 |
| Left side of the equation = | 4 | ( | 500 | − | 10 | x | ) | + | 1 10 | x | ( | 500 | − | 10 | x | ) |
| = | 4 | × | 500 | − | 4 | × | 10 | x | + | 1 10 | x | ( | 500 | − | 10 | x | ) |
| = | 2000 | − | 40 | x | + | 1 10 | x | ( | 500 | − | 10 | x | ) |
| = | 2000 | − | 40 | x | + | 1 10 | x | × | 500 | − | 1 10 | x | × | 10 | x |
| = | 2000 | − | 40 | x | + | 50 | x | − | 1 | x | x |
| = | 2000 | + | 10 | x | − | 1 | x | x |
| 2000 | + | 10 | x | − | 1 | x | x | = | 800 |