A can do a work in 15 days, B in 20 days, and C in 30 days. They all start the work together but C leaves after 5 days. How many more days will A and B take to complete the remaining work?
Show answer & explanation
Correct answer: B
Explanation
Efficiency of A = 1/15
Efficiency of B = 1/20
Efficiency of C = 1/30
Combined efficiency of all three = 1/15 + 1/20 + 1/30
= (4 + 3 + 2)/60 = 9/60 = 3/20
Work done in 5 days = 5 × (3/20) = 3/4
Remaining work = 1 − 3/4 = 1/4
Efficiency of A + B = 1/15 + 1/20
= (4 + 3)/60 = 7/60
Time to complete the remaining 1/4 work = (1/4) ÷ (7/60)
= 60/28 = 15/7 days
= 2 days + 1/7 day
= 2 days + 24/7 hours
= 2 days + 3 hours + 3/7 hour
= 2 days + 3 hours + 180/7 minutes
= 2 days + 3 hours + 26 minutes