December 2010 LSAT Section 4 Question 7

Which one of the following could be the color combinations of the glass in the three windows?

MadisonVanNatter on August 9, 2022

P or O in every group

Hello I was watching one of the question explanations and one of the deductions made was that O or P has to be in every group, but the video didn't explain that deduction a lot so I was wondering if you could go into more detail about that deduction because as I was working through the set I believe an acceptable group layout is 1: GPY 2:GR 3:OR.

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Emil-Kunkin on January 15 at 03:39PM

This is an implication of the final rule. The final rule is that if not p then o, and the contrapositive of this is that if not o then p. This means that at least one of o or p must always be in. In other words, they cannot both be out.