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PrepTest 78, Game 2, Question 7


This is the second question from PT 78, Game number 2. And it says, Mollie must be assigned to 1922 if which one of the following is true? So this is a global question where the right answer if true, is gonna force Mollie to go into 1922. Now, since we don't get any new information for this question, all we can do is go to the answer choices and try each answer choice to see if that answer would force Mollie to go into 1922.

If we can put Mollie somewhere else besides 1922, then that answer is not gonna be correct because it doesn't force her into that spot. So, let's take a look. A says, L is assigned to 1924. Now if you put L in 1924, then that means the third spot is gonna have to be T. Now, based on rule number 3, if T is in, then you're gonna have to have R.

And so that's why I'm gonna put R over here. Then if R is in, then that brings O immediately before it, but you can clearly see M isn't even in when L is assigned in 1924. So, A is not gonna be the answer. Answer choice B says, O was assigned in 1921. And so let's see, if we put O in 1921, what's the next thing that happens?

Well, the issue here is we actually have choices. We don't have to put the Mollie in 1922. You could actually put the Mollie out right now, and if you recall the diagram that we drew for answer choice A, you'll see that that actually works. You could put R in 2, you could put L in 4, and you could put LT in 3. And so notice that this situation, the very same diagram we drew for answer choice A proves that if you put O in 1921, like we did over here, that doesn't automatically force Mollie into 1922.

So, that's why B is not gonna be correct. Now, if you're tempted by answer choice B, that's probably because after you put O in number 1, what you did was you tried to put Mollie in 1922. And then you figured out well, doesn't that work? You could put Mollie in 1922, right? You could just make this an L and then you could make number 4 a Y.

And the issue is, yeah, that does work, you could put Mollie in 1922 when always in 1921, but that doesn't force Mollie to have to be assigned in 1922. You didn't have to put her in 1922. You could have put her as I showed before, you could have put her out and that's why B is not. C says, O was assigned in 1924.

Let's see, does that force Mollie into 1922? If O is in 4, then that means you can't have R in anymore, because if you put R in, you have to put O immediately before R. But O is in the last spot right now. So, R is gonna have to go out. And then based on the contrapositive of rule 3, if R is out that means T is out.

So that means slot number 3 is gonna have to be an L. And at this point, we have an M and we have a Y left. Now the issue is, you could put this M in either number 1 or number 2. Mollie is not forced to go to number 2. She could go to number 1 right now. And that's why answer choice C is not correct.

Again, if you were tempted by answer choice C, that's probably because you tried to put Mollie in 1922 and then you saw that it works, but simply showing that something could be true does not prove that it must be true. Answer choice D says, T is assigned to 1923. And here, if you put T in 1923 according to rule number 3, that means you have to have an R in and that means R is gonna go to 2 because it needs room for the O immediately before the R based on rule number 4.

Already you can see Mollie's not in 1922 right now. So, D is not gonna be correct. The correct answer must be answer choice E. Let's see why it works. If Y is assigned 1921, I'm gonna go ahead and put a Y over here. And at this point, you must realize that the R can no longer go in right now.

Because if you put the R in, you have to put an O immediately before it. But you can't put the R in 2, with an O before it now that the Y is in 1. So that's why R is gonna have to go out right now. And then if R is out based on rule number 3, the contrapositive, that means T also has to go out. This means that our third spot which was originally L/T has to be the L because the T is out.

And now our final two letters left are the M and the Y. Because the M cannot go in slot number 4 based on the second rule. That's why M is forced to go to 2 and the Y is in 4. So, answer choice E if true does force Mollie to go to 1922. That's why it's correct.

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