A and B can complete the work in 15 days and 20 days, respectively. They start together, but every 3rd day, B is absent. In how many days will the work be completed?
Show answer & explanation
Correct answer: A
Explanation
Given:
A completes the work in 15 days.
B completes the work in 20 days.
B remains absent every third day.
A's daily work capacity = 1/15
B's daily work capacity = 1/20
Work done on the 1st day = 1/15 + 1/20 = 7/60
Work done on the 2nd day = 1/15 + 1/20 = 7/60
Work done on the 3rd day = 1/15
Total work done in 3 days = 7/60 + 7/60 + 1/15 = 3/10
Work done in 9 days = 3 × 3/10 = 9/10
Remaining work = 1 − 9/10 = 1/10
Work done on the 10th day = 7/60
Remaining work = 1/10 − 7/60
= 6/60 − 7/60
Therefore, the work will be completed in days.