Problem number 13. There are 8 cars waiting in a line for the ferry. Each car contains either 2 or 3 people. There are 19 people in total waiting for the ferry. How many cars contain exactly 2 people? To solve this problem, I'm going to guess and check, and make a chart to keep track of my guesses. So there's a certain number of cars with 2 people, and there's a certain number of cars with 3 people. And the total needs to be 19 people. 19 is not a multiple of 2 because it's not even, and it's not a multiple of 3. So the answer is not going to be that all the cars have 2 people in them or all the cars have 3 people in them. So let's start checking by seeing if maybe there's 1 car with 2 people in it. If there's 1 car with 2 people in it, then there are 2 people in this car. And since we know that there are 8 cars, that would mean that there are 7 cars with 3 people in them. And that would mean that there are 7 times 3 or 21 people in these 7 cars. Let's add the number of people together. We have 2 and 21, which gives us 23, which is too many people. So our guess of 1 car with 2 people in it is not correct. Also, if we look at the answer choices, we see this is not one of the answer choices. Next, let's see if there are 2 cars with 2 people in them. 2 times 2 is 4. And if there are 2 cars with 2 people, that would leave us with 6 cars with 3 people. 6 times 3 is 18. So we have 4 plus 18 people, 22 people total. It's still not the right number. Let's try 3 cars with 2 people. 3 times 2 is 6 people. That would leave us 5 cars with 3 people. 5 times 3 is 15. And 6 plus 15 is 21. So still not right. There are 4 cars with 2 people. Make 8 people here. And that would mean that there are 4 cars with 3 people. Make 12 people here. 8 plus 12 is 20. What if we say that there are 5 cars with 2 people? 5 times 2 is 10. That gives us 10 people. And since there are 8 cars, that would leave 3 cars with 3 people. 3 times 3 is 9 people. 10 people plus 9 people is 19 people. Now let's double check what the problem is asking. How many cars contain exactly 2 people? 5. So the answer is D.

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