| 20 | x | × | 50 | + | 2800 | = | ( | 100 | − | x | ) | × | 80 |
| Left side of the equation = | 1000 | x | + | 2800 |
| 1000 | x | + | 2800 | = | ( | 100 | − | x | ) | × | 80 |
| Right side of the equation = | 100 | × | 80 | − | x | × | 80 |
| = | 8000 | − | x | × | 80 |
| 1000 | x | + | 2800 | = | 8000 | − | 80 | x |
| 1000 | x | + | 80 | x | = | 8000 | − | 2800 |
| 1080 | x | = | 8000 | − | 2800 |
| 1080 | x | = | 5200 |
| x | = | 5200 | ÷ | 1080 |
| = | 5200 | × | 1 1080 |
| = | 130 | × | 1 27 |
| x | = | 130 27 |
| x | = | 4.814815 |