| ( | 100 | − | x | ) | ÷ | ( | 90 | − | x | ) | = | 10 |
| Multiply both sides of the equation by: | ( | 90 | − | x | ) |
| ( | 100 | − | x | ) | = | 10 | ( | 90 | − | x | ) |
| 100 | − | x | = | 10 | ( | 90 | − | x | ) |
| 100 | − | x | = | 10 | × | 90 | − | 10 | x |
| 100 | − | x | = | 900 | − | 10 | x |
| - | x | + | 10 | x | = | 900 | − | 100 |
| 9 | x | = | 900 | − | 100 |
| 9 | x | = | 800 |
| x | = | 800 | ÷ | 9 |
| = | 800 | × | 1 9 |
| x | = | 800 9 |
| x | = | 88.888889 |