Machine A can produce 100 widgets in 5 hours. Machine B can produce 100 widgets in 4 hours. If they work together, how many hours will it take to produce 225 widgets?

✓ Correct Answer: Option C

Machine A's rate = 100/5 = 20 widgets/hour. Machine B's rate = 100/4 = 25 widgets/hour. Combined rate = 20 + 25 = 45 widgets/hour. Time = Total widgets / Combined rate = 225 / 45 = 5 hours.