## PrepTest 79, Game 4, Question 20

### Transcript

Question number 20 is a local question asking if T did not transmit to any other computer, which one of the following must be true? So the condition is T cannot transmit to anyone else. That means T is going to get the virus from someone else and there's nothing that T can pass to. So let's start by looking at the rules and mention T in particular rules four and five.

If T doesn't pass to anyone else, that means T can't be passing to Q, and T can't be passing to P. So for this problem, we know R goes to Q, and U goes to P. So let me just go ahead and put in R goes to Q like this. Off to the side all right, U goes to P, and it's not totally clear what we can do with this U,P relationship right now.

So at this point we know that U transmits to P. And we also have to account for this T. Those are the three letters left, U, P and T. Well, since T can't transmit to anyone for this problem, that means T cannot go in this spot. And if T can't go in this spot, then the only candidate left is P.

You couldn't put the U over here because then you would have to transmit to R, S and then also P. And the first rule says you can't have a computer transmitting to three other computers. So we know that P has to be the one that transmits to R and S. U have to be the one that transmits to P.

And that means that the T has to go over here, because S has to transmit to somebody, that was rule number two, and the only person left is T. So we're looking for what must be true, answer choice A, says P transmits to S. This is our answer because we know P must transmit to S. Answer choice B gets it backwards. It says Q transmits to R but it's the other way around.

The answer choice C says U transmits to S but actually no, U transmits to P. It's the P that transmits to S. D, says P doesn't transmit to anyone, but actually no, P must transmit to both R and S. E, says R doesn't transmit to anyone, but no, R has to transmit to Q.