A can complete a piece of work in 20 days, and B can do the same work in 30 days. If they work together for 5 days, what fraction of the work remains to be done?
Show answer & explanation
Correct answer: A
Explanation
A's 1-day work efficiency = 1/20
B's 1-day work efficiency = 1/30
Combined 1-day work efficiency of both = 1/20 + 1/30
= (3 + 2)/60
= 5/60
= 1/12
Work done in 5 days = 5 × 1/12
= 5/12
Remaining work = 1 - 5/12
= 7/12