A monkey climbs on 45 m high greased pole. In first minute he climbs 5 meter and 2nd minutes he comes down by 1 meter. If he climbs in such a manner in what time will he comes to the height of pole.

21 min

In 1st min ⇒ climes by 5 mtr

In 2nd min ⇒ comes down by 1 mtr

Therefore,

In 2 min ⇒ climes by 4 mtr

In 20 min ⇒ climes by 40 mtr, and

in next min he jumps by 5 mtr and reach the height of the pole.

Therefore, total time taken = 21 min