P and Q can do a piece of work in 10, and 6 days, respectively, while R can destroy the same work in 15 days. If P and Q work on 1st day, R works on 2nd and so on. They follow the same pattern until the work gets completed. How many days will it take for the work to be completed the first time?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e.
Total work = 30 units (LCM of 10, 6, 15).
P’s efficiency = 3, Q’s efficiency = 5, R’s efficiency = -2 units/day
Every 2 days = 8 − 2 = 6 units done
After 8 days = 24 units done and 6 units left
On 9th day ,P+Q do 8 units → need 6/8 = 3/4 day
Work is completed in days