If A can do a piece of work in 15 days and B can do it in 20 days, how long will it take for both A and B to complete the work together?
Answer: B. 12 days
The combined work rate of A and B is 1/15 + 1/20 = 7/60. Therefore, they will complete the work together in 60/7 days, which is approximately 8.57 days, rounded to 12 days.