A can do a piece of work in 10 days, and B can do the same work in 20 days. With the help of C, they finished the work in 4 days. C can do the work in how many days, working alone?

Question: A can do a piece of work in 10 days, and B can do the same work in 20 days. With the help of C, they finished the work in 4 days. C can do the work in how many days, working alone?Solution:A and B's combined 4 day work = 4(1/10 + 1/20) = 4(3/20) = 12/20 = 3/5.Remaining work = 1 - 3/5 = 2/5This means C did 2/5 work in 4 days, hence he can finish the complete work in (5/2) × 4 = 10 days.