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#32028
Please post below with any questions!
 soobin903
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#75491
Hello, Powerscore,

As the videos have been removed, and as you posted in a separate posting that you would NOT recommend that we reach the answer by listing all nine of the solutions,
which method would you recommend for determining the virus transmission sequence?
I had narrowed down my choices to C and D, as I had ruled out A,B,E from the answer choices, but could not really determine which of the two would be the correct answer.

Thank you in advance!
 Luke Haqq
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#75571
Hi soobin903!

Great question!

First, in terms of general strategy, this question comes as the second to last in the games section. Depending on how you approach the logic games section (some people choose to do them out of order), that might mean there was little time left by the time you got to this question. Given that you note that you were down to choosing between (C) and (D), it's therefore worth noting how you might have opted for the correct answer, (C), even without diagramming anything at all.

Namely, between those two choices, look at the difference between the extent to which these variables are constrained. The question asks for which option would completely determine the others. In answer (D), the variables are U and P. These two variables show up only in one of the game's rules. By contrast, answer (C) refers to T and S, which appear in four rules combined. This strongly suggests that T and S would be much more constrained--that is, what happens to them would be more decisive as to what happens to the rest of the variables. Since this question asks for a complete determination, one might therefore have guessed (C) over (D), since the variables T and S are more decisive and connected to other variables through multiple rules.

Second, one can see more specifically why (C) is the correct answer. That answer choice states, "T transmitted the virus to S." As shorthand, we can represent this as:

T :arrow: S

The game also provides us with a connected rule: "The computer that transmitted the virus to R also transmitted it to S." Since we know that T is the computer that transmitted the virus to S, we therefore know that T is also the computer that transmitted it to R. We also know that T only transmitted it to S and R, because of the rule, "No computer transmitted the virus to more than two other computers on the network." We therefore have:

T :arrow: S
and
R
The game also includes a rule that "Either R or T transmitted the virus to Q." We know that T not transmit to Q, because we already know T transmitted to a max of S and R. Since it could not be T, we therefore would know that R transmitted the virus to Q. We could therefore add:

T :arrow: S
and
R :arrow: Q
Finally, a rule tells us that Either "T or U transmitted the virus to P." Again, since we know T transmitted only to S and R, then we know that U transmitted to P (U :arrow: P). However, it might not be clear where this U :arrow: P block would go. We ultimately know it must go after S because we are given the rule that "S transmitted the virus to exactly one other computer on the network" (which could not be T, R, or Q), and the rule that " Each computer received the virus exactly once" (since P already receives it from U, we know that P does not also receive it from S). This leaves us with a sole option--U is the only other computer that S transmits to, or:

T :arrow: S :arrow: U :arrow: P
and
R :arrow: Q
If we started from a given that T transmitted to S, in other words, all of the other variables would be determined.

Hope that helps!

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