A and B can complete a work in 20 days. If A works alone for 5 days and then B joins him, how many more days will they take to finish the work?
Answer: D. 8 days
A completes 1/20 of the work in 5 days. The remaining work is 19/20. A and B together can complete the work in 10 days, so they will take 8 days to finish the remaining work.