A and B can complete a piece of work in 12 days. If A works alone for 4 days and then B works alone for 8 days, how many days will it take for A and B to finish the remaining work together?
Answer: A. 2 days
A and B together complete 1/12 of the work per day. In 4 days, A completes 4/12 of the work. B then works for 8 days, completing 8/12 of the work. Together they have completed 12/12, so no remaining work is left.