If A can finish a work in 24 days and B can finish the same work 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
After working together for 12 days, A and B complete 12*(1/24 + 1/36) = 1/4 of the work. A will then take 18 days to finish the remaining 3/4 of the work.