| ( | 10 | X | + | 20 | ) | ÷ | ( | X | + | 20 | ) | = | 5 | ÷ | 2 |
| Multiply both sides of the equation by: | ( | X | + | 20 | ) |
| ( | 10 | X | + | 20 | ) | = | 5 | ÷ | 2 | × | ( | X | + | 20 | ) |
| 10 | X | + | 20 | = | 5 | ÷ | 2 | × | ( | X | + | 20 | ) |
| 10 | X | + | 20 | = | 5 | ÷ | 2 | × | X | + | 5 | ÷ | 2 | × | 20 |
| 10 | X | + | 20 | = | 5 2 | X | + | 50 |
| 10 | X | − | 5 2 | X | = | 50 | − | 20 |
15 2 | X | = | 50 | − | 20 |
15 2 | X | = | 30 |
| X | = | 30 | ÷ | 15 2 |
| = | 30 | × | 2 15 |
| = | 2 | × | 2 |
| X | = | 4 |