A can do a job in 12 days B in 18 days. A works for 3 days then B joins. Total days to finish?
Show answer & explanation
Correct answer: A
Explanation
A completes the work = 12 days
B completes the work = 18 days
A works alone for the first 3 days
Work done in 1 day = 1 / Number of days
A's efficiency per day = 1/12
Work done by A in 3 days = 3/12 = 1/4
Remaining work = 1 − 1/4 = 3/4
Combined efficiency of A + B = 1/12 + 1/18 = (3 + 2)/36 = 5/36
Time required to complete the remaining work = (3/4) ÷ (5/36) = 3/4 × 36/5 = 27/5 = 5.4 days
Total time = 3 + 5.4 = 8.4 days