| ( | 300 | + | X | ) | ÷ | ( | 100 | + | X | ) | = | 99 100 |
| Multiply both sides of the equation by: | ( | 100 | + | X | ) |
| ( | 300 | + | X | ) | = | 99 100 | ( | 100 | + | X | ) |
| 300 | + | X | = | 99 100 | ( | 100 | + | X | ) |
| 300 | + | X | = | 99 100 | × | 100 | + | 99 100 | X |
| 300 | + | X | = | 99 | + | 99 100 | X |
| X | − | 99 100 | X | = | 99 | − | 300 |
1 100 | X | = | 99 | − | 300 |
1 100 | X | = | - | 201 |
| X | = | - | 201 | ÷ | 1 100 |
| = | - | 201 | × | 100 |
| X | = | - | 20100 |