Machine A can complete a task in 10 hours, and Machine B can complete the same task in 15 hours. If they work together, what fraction of the task will they complete in 3 hours?

✓ Correct Answer: Option C

Machine A's rate is 1/10 task/hour. Machine B's rate is 1/15 task/hour. Their combined rate is (1/10) + (1/15) = (3/30) + (2/30) = 5/30 = 1/6 task/hour. In 3 hours, they will complete 3 * (1/6) = 1/2 of the task.