A can do a work in 30 days, B can do it in 45 days, and C can do it in 60 days. If they work together, how long will it take them to complete the work?
Answer: B. 12 days
The combined rate of A, B, and C is 1/30 + 1/45 + 1/60 = 1/10. Therefore, they will complete the work in 10 days.