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Bunuel
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sidisking
I don’t quite agree with the solution. How do we know that there are only red and electric cars at the factory? Couldn't it be true that there are blue cars?

Blue cars fall into Neither category.
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How about this one?
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I used this method.
Bunuel
Official Solution:


If a car is randomly selected from a factory's production line, what is the probability that the selected car is electric?

This question is essentially about overlapping groups framed as a probability problem. We use the formula:

Total = Electric + Red - Both + Neither

Our goal is to calculate Electric/Total * 100. To make calculations easier, let's assume Total = 45 (the least common multiple of the denominators from the statements).

(1) The probability that a car selected at random is neither red nor electric is \(\frac{1}{3}\).

45 = Electric + Red - Both + 15

Not sufficient.

(2) The probability that a car selected at random is red but not electric is \(\frac{2}{15}\).

The above implies:

Red - Both = 6.

Not sufficient.

(1) + (2) Substituting Red - Both = 6 into 45 = Electric + Red - Both + 15, we get 45 = Electric + 6 + 15, which simplifies to Electric = 24. Therefore, Electric/Total * 100 = 24/45 * 100. Sufficient.

Answer: C
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Why the second statement represents Red - Both?
I didn't understand why finding the prob that a car is red but not eletric, makes you find the probability of both.
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Why the second statement represents Red - Both?
I didn't understand why finding the prob that a car is red but not eletric, makes you find the probability of both.

Because "red but not electric" means the car is red and not electric, so you're excluding the overlap: red AND electric.

That means you're counting only the red cars that are not also electric.

So mathematically, it's: Red total - Both.

That’s why the probability in Statement (2) represents Red - Both.
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