October 2010 LSAT Section 4 Question 12

Which one of the following could be the order in which the runners run, from first to fourth?

JosephB on March 8 at 08:47PM

Isn't rule 4 invalid?

3. If not U then R2 4. R2 then not U. That's just reversing which is invalid, right? Will that affect the way the game is played? Does invalid not apply to logic games?

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Emil-Kunkin on March 12 at 02:46AM

You're right that we can't deduce rule 4 from rule 3. However they can be independently true. You're not allowed to assume that rule four is true because rule 3 is true. However we know that rule four is true because it is rule four.

The technical term for this is a biconditional (don't worry about the terminology) which just means that two things always must go together. That is that if one is present then the other is as well, and if one is absent then the other is as well.