Question

A monkey climbs 30 feet at the beginning of each hour and rests for a while when it slips back 20 feet before it again starts climbing at the beginning of the next hour. If he begins his ascent at 8:00 am, at what time will he first touch a flag at 120 feet from the ground?

• A. 5 p.m.
• B. 9 p.m.
• C. 6 p.m.
• D. 8 p.m.

Hint:

In problems involving climbing or descending, account for the net progress made during each cycle (climb and slip).

Answer 1

The Correct Option is C

In the first hour, the monkey climbs 30 feet, but slips back 20 feet, so effectively climbs \( 30 - 20 = 10 \) feet each hour. After 11 hours, the monkey will have climbed \( 10 \times 11 = 110 \) feet. In the 12th hour, the monkey climbs 30 feet and reaches a total of \( 110 + 30 = 140 \) feet. Since it only needs to reach 120 feet, it will touch the flag at some time during the 12th hour. Thus, the monkey will touch the flag at \( 8:00 + 5 \text{ hours} = 6:00 \) p.m.