#7 - A certain retailer promotes merchandise by using the

[Administrator]

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
  
  excess

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

[rameday]

How would I diagram this? At all times there is either a managers sale or a holiday sale or both going on?

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

A

[Jon Denning]

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 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 simultaneously...it merely rules out the option of them both being removed.

Hope that helps!

[hoyasaxa21]

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!

Chris

[Paul Marsh]

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 no excess merchandise
(E) Mistakenly Reverses that to say:
No excess merchandise 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 B
A Mistaken Reversal of our conditional would be:
B A
And a Mistaken Negation of our conditional would be:
NOT A NOT B

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

[Laurenw3692!]

Hi!

How would I know to diagram the last sentence like I'm supposed to for future questions? Since, I don't think there were any indicator words. Basically how do I not do a mistaken reversal or mistaken negation on problems like this? I know now this is how it should be diagrammed:
In August, there is no holiday and no excess
August ---> no excess and no holiday
But I think I did the reversal: if there are no holidays and no excess it is not august

Thank you!!

[Jeff Wren]

Hi Lauren,

There actually are indicators words here, although they aren't from the common list of sufficient and necessary indicators.

The two indicators here are the negative conditional words "no" and "never." These words often show up in grouping games. For example, a rule might state, "A and B are never selected together."

There are two different ways to diagram these statements.

The standard way would be to diagram using the regular (one way) conditional arrow and putting the "negative" on the necessary condition term.

For example,

A -> not B

and the contrapositive would be (if B -> not A)

It's important to note that the negative term appears in the necessary condition and not the sufficient.

You can also use what we call the double-not arrow, which is a way of representing both the original diagram and contrapositive in one "super" diagram.

Using the double-not arrow, it would be:

A <- | -> B

This basically shows that A and B can never go (or occur) together.

This concept is discussed in Lesson 5 of The PowerScore LSAT Course and in chapter 6 of "The Logical Reasoning Bible."

[Hyunuk Park]

The last sentence confirms that in August, no sale is to occur.
But doesn't D cover any month, if selected, would have either of the sale?
Thus, D looks like it doesn't sufffice being must be valid always.
Help me, what am I missing?

[Jeff Wren]

Hi Hyunuk,

You wrote, "The last sentence confirms that in August, no sale is to occur."

Try going back and rereading the last sentence (and the other sentences in the stimulus too) very carefully. No where does the last sentence confirm that there is no sale in August. In fact, from the first sentence of the stimulus, we know that every month must have a sale, either a "manager's sale" or a "holiday sale," or both. This is indicated by the words "at all times," meaning no exceptions.

The way the words "either/or" are used on the test means that at least one of the two things must happen. For example, the statement "either A or B" means "if A does not happen, then B must happen" and by the contrapositive, "if B does not happen, then A must happen."

Since either a "manager's sale" or a "holiday sale" must always happen, when one doesn't happen, the other must happen. This is true for any month, including August. This directly proves Answer D.

As for August, what the stimulus states is that there is no holiday in August and no excess merchandise. However, these facts in no way indicate that there is no sale in August. Nothing in the stimulus indicates when sales are not going on, only certain conditions when we know for certain that a particular sale is going on. It looks like you may be making a Mistaken Negation. These conditions (holidays, excess merchandise) are sufficient for the sales, not necessary.