A frog is at the bottom of the well which is 20 meters deep. Everyday the frog jumps 5 meters upwards and fall 4 meters down.On which day the frog will reach the top?
Is reaching to top considerd to be when the frog falls back 4 meters and his height is 20 m from the bottom?
if so, then each day he gains 1 meter in height ..... it will take 20 days. Not that for several days the frog's 5 meter jump will raise it higher than the lip of the well....but the frog falls back down.....
going off your answer, if the frog DID reach the top the moment it goes over the well top, regardless how much it falls:
the well is 20m deep, the frog jumps 5m. So the frog needs to reach 20 - 5 = 15m.
jumps 5m and falls 4m, so it jumps 5 - 4 = 1m
the frog reaches the top on the 15th day