If A can complete a work in 24 days and B can complete it in 36 days, how long will it take for A to finish the work alone after working with B for 12 days?
Answer: B. 18 days
In 12 days, A and B together complete 1/24 + 1/36 = 1/15 of the work. Therefore, they complete 12/15 of the work, leaving 3/15. A alone can finish the remaining work in 18 days.