| 200 | ÷ | ( | 1 | + | r | ) | − | 1 | = | 180 |
| Multiply both sides of the equation by: | ( | 1 | + | r | ) |
| 200 | − | 1 | ( | 1 | + | r | ) | = | 180 | ( | 1 | + | r | ) |
| 200 | − | 1 | × | 1 | − | 1 | r | = | 180 | ( | 1 | + | r | ) |
| 200 | − | 1 | × | 1 | − | 1 | r | = | 180 | × | 1 | + | 180 | r |
| 200 | − | 1 | − | 1 | r | = | 180 | + | 180 | r |
| 199 | − | 1 | r | = | 180 | + | 180 | r |
| - | 1 | r | − | 180 | r | = | 180 | − | 199 |
| - | 181 | r | = | 180 | − | 199 |
| - | 181 | r | = | - | 19 |
| 19 | = | 181 | r |
| 181 | r | = | 19 |
| r | = | 19 | ÷ | 181 |
| = | 19 | × | 1 181 |
| r | = | 19 181 |
| r | = | 0.104972 |