Three friends can complete a puzzle in 4 hours. If they invite two more friends to help, how long will it take to complete the same puzzle?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is Option 4 i.e. 144 minutes.
The three friends can complete the puzzle in 4 hours
Therefore, their combined work rate is 1/4 of the puzzle per hour
Let R be the work rate of each person then,
⇒ 3R = 1/4
⇒ R = 1/12
So, each friend can complete 1/12 of the puzzle per hour
Now,
⇒ 5R = 5/12
⇒ T = 1/5R
⇒ T = 1/5/12
⇒ T = 12/5 = 2.4 hours or 144 minutes