A can do a piece of work in 10 days and B can do it in 15 days. In how many days will they finish the work together?
Answer: B
A's one day's work = 1/10. B's one day's work = 1/15. Together, their one day's work = \(1/10 + 1/15 = (3+2)/30 = 5/30 = 1/6\). So, they will finish the work together in 6 days.