| ( | 60 | + | X | ) | ÷ | ( | 65 | + | X | ) | = | 99 100 |
| Multiply both sides of the equation by: | ( | 65 | + | X | ) |
| ( | 60 | + | X | ) | = | 99 100 | ( | 65 | + | X | ) |
| 60 | + | X | = | 99 100 | ( | 65 | + | X | ) |
| 60 | + | X | = | 99 100 | × | 65 | + | 99 100 | X |
| 60 | + | X | = | 1287 20 | + | 99 100 | X |
| X | − | 99 100 | X | = | 1287 20 | − | 60 |
1 100 | X | = | 1287 20 | − | 60 |
1 100 | X | = | 87 20 |
| X | = | 87 20 | ÷ | 1 100 |
| = | 87 20 | × | 100 |
| = | 87 | × | 5 |
| X | = | 435 |