September 2016 LSAT Section 3 Question 23

# If P is the only computer that transmitted the virus to two other computers on the network, which one of the followin...

Replies

Ben on December 18, 2019

Hi Ryan, thanks for the question!The idea is that if P is the only computer that transmits to two others, then it must transmit to both R and S. This is because R and S must get the virus from the same computer.

Then we have two options that can give the virus to P. This is computers T and U. We can create two diagrams. One in which T - P. One in which U - P.

So now we have the following:

T - P - R and S, (in this scenario, R must give the virus to Q because T cannot anymore. So R gives it to Q and S gives it to U)

U - P - R and S (in this scenario, S must give the virus to T because it cannot give it to the leftover Q. The remaining Q can receive the virus from R or T)

This gives us 3 diagrams to answer our question.

T - P - R - Q

- S - U

U - P - R - Q

- S - T

U - P - R

- S - T - Q

In all scenario, Q is last (answer choice C)

Answer choice A is incorrect because it is possible that S transmits the virus to U. (First diagram).

I hope this helps. Please let me know if you have any other questions!

on June 24, 2020

How do you know that a computer must give it to P? Couldn't there be more diagrams if P was the first infected? or am I overlooking a rule here?on June 24, 2020

Nevermind.