P alone can complete a piece of work in 10 days, while Q alone can complete the same piece of work in 15 days. To complete the work in 4 days, R is hired by P and Q. How many days does R take to complete the work alone?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 12 days.
Let R alone complete the work in x days
So, (1/10) + (1/15) + (1/x) = 1/4
⇒ (1/x) = (1/4) - (1/10) - (1/15) = (1/12)
⇒ x = 12
Hence, R takes 12 days to complete the work alone.