#9 - Local, Justify

[Dave Killoran]

Complete Question Explanation
(The complete setup for this game can be found here: lsat/viewtopic.php?f=351&t=3899)

The correct answer choice is (A)

Note that this is a Justify question, wherein you must supply the answer choice that forces the desired result, which in this case is to have only one possible solution.

Looking over our setup, when we added the contrapositive of the third rule to the original first rule, the following resulted:

G2-Q9-d1.png

Thus, if an answer stipulated that light 1 was purple, that would result in a single color sequence. As it happens, answer choice (A) indicates that light 1 is purple, and answer choice (A) is thus correct.

Note that this question can also be easily solved using hypotheticals.

[wwarui]

Hello,

Question Number 9

Please explain this question and illustrate why answer A is correct. I have tried but it does not seem to work. Why would the colour sequence be purple when it clearly states in the stimulus that "Whenever light 1 is purple, light 2 is yellow".
Thanks!!

[Emily Haney-Caron]

Hello,

Here, we're looking for an answer where we have only one possible solution to the game. The question isn't asking for an answer where all three lights will be the same color; rather, we're just trying to find an answer that only leaves one possibility for the other two light colors.

A does that. If light 1 is purple, we know from Rule 1 that light 2 is yellow. We also know from rule 3 that if light 1 is purple, then light 3 cannot be purple or yellow, since rule 3 would then require that light 2 be purple (but we know light 2 is yellow). Therefore, light 3 has to be green if light 1 is purple.

Therefore, if light 1 is purple, the sequence is P-Y-G.

[wwarui]

Hi Emily:

Gosh! I completely misunderstood the question. Thank you for clarifying this. No wonder I couldn't figure it out.
THANKS!!!