Question

A monkey climbs 30 feet at the beginning of each hour and rests for a while when he slips back 20 feet before he again starts climbing in the beginning of the next hour. If he begins his ascent at 8.00 a.m., at what will he first touch a flag at 120 feet from the ground?

• A. 4 p.m.
• B. 5 p.m.
• C. 6 p.m.
• D. 8 p.m.

Hint:

When solving repetitive motion problems, analyze the net movement per cycle and separately account for the final step.

Answer 1

The Correct Option is C

Step 1: Understanding the climb pattern
- The monkey climbs 30 feet in the first hour but slips back 20 feet. - Net gain per hour = \( 30 - 20 = 10 \) feet.
Step 2: Calculate the hours required
- To reach 120 feet, in the last hour, the monkey climbs 30 feet directly. - Before the last hour, he must cover \( 120 - 30 = 90 \) feet. - Since he gains 10 feet per hour, time required to reach 90 feet = \( 90 \div 10 = 9 \) hours. - The last climb happens in the 10th hour.
Step 3: Compute the time
- Starting at 8:00 a.m., reaching 90 feet takes 9 hours, i.e., 5:00 p.m. - The final climb happens in the 10th hour, at 6:00 p.m.
Thus, the correct answer is 6 p.m.