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Complete Question Explanation

Must Be True—SN. The correct answer choice is (D)

This stimulus presents several conditional statements regarding a certain store's policy concerning sales:

At all times there is either a managers sale, or a holiday sale, or both:
  • no manager's sale → holiday sale

    no holiday sale → manager sale
If a manager wishes to clear out a line of merchandise, they have a manager's sale:
  • manager wishes to clear → manager's sale
If a holiday falls within a given month and there is excess merchandise, they have a holiday sale:
  • holiday

    and .......... holiday sale

In August, there is no holiday and no excess:
  • ..... ..... ..... no holiday

    August .......... and

    ..... ..... ..... no excess
The question stem is a Must Be True, so the right answer choice should be confirmed by the conditional statements above.

Answer choice (A): This answer choice is not supported by the passage; all we can say is that if there is excess in any holiday month, there will be a holiday sale. If there is no excess, we have no information on what the store will do.

Answer choice (B): This incorrect answer choice is unsupported by the stimulus, as there may be other months without holidays, and other holiday months without excess.

Answer choice (C): We know that this is unsupported; there could still be excess merchandise, and there could still be a concurrent holiday sale as well.

Answer choice (D): This is the correct answer choice, confirmed by the first conditional rule presented in the stimulus: there is always either a managers sale, or a holiday sale, or both.

Answer choice (E): This is a mistaken negation of a portion of the final conditional rule. According to the stimulus, if it is August there is no excess: ..... August → no excess

This choice incorrectly asserts a mistaken reversal: ..... no excess → August
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How would I diagram this? At all times there is either a managers sale or a holiday sale or both going on?

MS :dblline: HS I know this means one or the other but not both.

 Jon Denning
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Hey rameday,

You're close! The fact that at least one must always be occurring means that they can't both be absent, hence we'd show it as follows:

..... MS :dblline: HS

What that means is that if one is not present/happening, the other must be. By default this also allows the possibility of them happening merely rules out the option of them both being removed.

Hope that helps!
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Good afternoon,

Does answer choice (E) assert a mistaken negation or a mistaken reversal of a portion of the final conditional rule?

Thank you very much, and have a great day!

 Paul Marsh
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Hi hoyasaxa! You're exactly right - Answer Choice (E) contains a Mistaken Reversal of the last sentence of the stimulus. That portion of the stimulus tells us, in August there is never excess merchandise.
August :arrow: no excess merchandise
(E) Mistakenly Reverses that to say:
No excess merchandise :arrow: August

So we can safely toss out (E), since it's a Mistaken Reversal.

Now, it seems like from your question you're wondering if this is also a Mistaken Negation. The answer is yes - Mistaken Reversals and Mistaken Negations are actually the same thing! Watch this. Let's say we have the conditional "If A, then B". We diagram that as:
A :arrow: B
A Mistaken Reversal of our conditional would be:
B :arrow: A
And a Mistaken Negation of our conditional would be:
NOT A :arrow: NOT B

But let's return to our Mistaken Reversal. B :arrow: A. What if we take the contrapositive of that Mistaken Reversal, what would that look like? Well it would be:
NOT A :arrow: NOT B

But wait a minute, that's the exact same as our Mistaken Negation! That's because Mistaken Reversals and Mistaken Negations are actually logically equivalent to each other. Remember that the contrapositive of a conditional is logically equivalent to that conditional. A Mistaken Reversal and a Mistaken Negation are just contrapositives of each other. They're the exact same Flaw - mistakenly confusing the sufficient and necessary conditions of a conditional. So don't get ever get hung up on "Oh is this a Mistaken Negation or a Mistaken Reversal?" It doesn't matter, because they're the same thing! An LSAT question will never ask you to differentiate between those two because (and I'm sorry to sound like a broken record here) they're logically identical! All you need to recognize is that an argument messed up by confusing the sufficient and necessary conditions.

Hope that helps!

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