Question

A monkey climbs 20 feet at the beginning of each hour and rests for a while when he slips back 5 feet before he again starts climbing in 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 110 feet from the ground?

• A. 2:00 PM
• B. 3:00 PM
• C. 4:00 PM
• D. 2:30 PM

Answer 1

The Correct Option is B

The monkey climbs 20 feet every hour but slips back 5 feet. Therefore, the net progress he makes each hour is:

20 − 5 = 15 feet per hour.

Now, let’s calculate when he first touches the flag at 110 feet.

• In the first hour, he climbs 20 feet, so he reaches a height of 20 feet.
• In the second hour, he climbs 20 feet again, but slips back 5 feet, so his net progress for the second hour is 20 − 5 = 15 feet. Now, he is at 20 + 15 = 35 feet.
• In the third hour, he climbs another 20 feet, but slips back 5 feet, making a net progress of 15 feet. Now, he is at 35 + 15 = 50 feet.
• Continuing this pattern, the monkey will reach 95 feet at the end of the seventh hour, after having climbed: 6 × 15 = 90 feet. He is at 95 feet at 3:00 PM.

At this point, when the monkey climbs 20 feet at the beginning of the eighth hour, he will reach 115 feet. Since he only needs to climb 15 feet to touch the flag at 110 feet, the monkey will reach the flag during the eighth hour. Therefore, the time when he first touches the flag is 3:00 PM.