A man starts climbing a hill every minute he ascended 20 yards but slips down 5 yards how long will he take to ascend a point 80 yards hight?

A man starts climbing a hill every minute he ascended 20 yards but slips down 5 yards how long will he take to ascend a point 80 yards hight?

Explanation

Man climbs 20 yards and slips down 5 yards in one minute

i.e. he climbs (20-5 = 15 yards) in one minute.

But in the last minute, he will be climbing 20 yards as he gets on the top so no slip.

Time taken to climb 80 yards = 60/15 + 1

                                                   = 5 minutes.

He climbs the hill in 5 minutes