-
A person observed that he required 30 seconds less time to cross a circular ground along its diameter than to cover it once along the boundary. If his speed was 30 m/minute, then the radius of the circular ground is (Take π = 22/7) :
-
- 5.5 m
- 7.5 m
- 10.5 m
- 3.5 m
- 5.5 m
Correct Option: D
Let the radius of circular field be r metre, then
| - | = | |||||
| 30 | 30 | 60 |
| ⇒ | - | = | ||||
| 15 | 15 | 2 |
| ⇒ πr - r = | ||
| 2 |
| ⇒ r(π - 1) = | ||
| 2 |
| ⇒ r |  | - 1 |  | = | ||
| 7 | 2 |
| ⇒ r × | = | |||
| 7 | 2 |
| ⇒ r = | = 3.5 metre | |
| 2 |
