A monkey, at the bottom of a well, begins climbing the wall. It climbs for one hour and rests the next hour. In one hour it climbs 4 meters. In the one hour it rests, it slips back 2 meters. If the height of the wall is 20 meters, then the time taken by the monkey to climb out of the well(in hours) is?

The monkey climbs 4m in one hour and slips 2m in the next, gaining 2m net every 2 hours. After 8 cycles (16 hours), it reaches 16m. In the next climb hour, it reaches 20m and climbs out before slipping back. So total time = 16 + 1 = 17 hours. The final climb hour doesn't need a subsequent rest hour since the monkey escapes.