A1 alone can do a work in 12 days and A2 alone can do the same work in 15 days. With help of A3, they finish the same work in 5 days. In how many days A3 alone can do the same work?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 20 days.
Given that
A1 alone can do a work in = 12 days
A2 alone can do the same work in = 15 days
A1, A2 and A3, they finish the same work in = 5 days
Total work = LCM (12, 15, 5) = 60
The efficiency of A1 = 60/12 = 5
The efficiency of A2 = 60/15 = 4
The combined efficiency of A1, A2 and A3 = 60/5 = 12
So, the efficiency of A3 = 12 - (5 + 4) = 3
Hence, A3 alone can do the same work in = 60/3 = 20 days