If A can do a work in 15 days and B can do the same work in 10 days, how many days will they take to complete the work if A works for 5 days and then B completes the remaining work?
Answer: C. 10 days
In 5 days, A completes 5/15 = 1/3 of the work. B needs to complete 2/3 of the work, which he can do in (2/3) * 10 = 20/3 days or approximately 6.67 days.