Answer:
You have 10 batteries of which 5 are dead. That means 1/2 of the batteries are dead. So if you randomly select a battery, there is a 50% chance of selecting a dead one, or a good one. But since you're choosing 2, that means the first one you select has a 50% chance of being dead or good, (5/10), but then the second one has a 44% chance of being dead or good, (4/9). multiplying these, you get 22% chance of randomly selecting 2 good batteries.
