A can complete a task in 15 hours, B can complete it in 10 hours, and C can complete it in 6 hours. If they all work together, how long will it take to complete the task?
Answer: B. 3 hours
Their combined work rate is 1/15 + 1/10 + 1/6 = 1/2. Therefore, they will complete the task in 2 hours.