A and B can do a piece of work in 30 days. B and C can do the same work in 24 days and C and A in 20 days. They all work together for 10 days then B and C leave. How many days more will A take to finish the remaining work?
Answer
Let total work be 120 units (LCM of 30, 24 and 20).
(A+B)'s one day work = 120/30=4 units
(B+C)'s one day work = 120/24=5 units
(C+A)'s one day work = 120/20=6 units
Adding all three equations,
2A+2B+2C=15
2(A+B+C)=15
A+B+C=7.5
SO,
(A+B+C)'s one day work = 7.5 units
A's one day work = (A+B+C)'s one day work-(B+C)'one day work=7.5 - 5 = 2.5 units
In 10 days, all three complete 75 (10×7.5) units of work.
Remaining 45 units can be completed by A in 18 days (at rate of 2.5 units per day).