Machine A can complete a task in 6 hours. Machine B can complete the same task in 10 hours. If both machines work together, how many hours will it take to complete 2/3 of the task?

✓ Correct Answer: Option B

Machine A's rate is 1/6 task/hour, B's is 1/10 task/hour. Combined rate: 1/6 + 1/10 = 8/30 = 4/15 task/hour. Time to complete 1 task is 15/4 hours. To complete 2/3 of the task: (2/3) * (15/4) = 30/12 = 2.5 hours.