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 time 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. None of these

Answer 1

The correct option is C $6$ p.m.

The monkey ascends $30$ feet and then descends by $20$ feet every hour. Consider the monkey ascends only $10$ feet an hour till it reaches $90$ ft. in $9$ hours.
Next time when he ascends $30$ ft it will touch the $120$ ft flag.
Thus, monkey takes $10$ hours to climb $120$ ft.
It starts at $8.00$ AM and hence reaches $120$ ft at $6$ PM