The only way that bookstores can profitably sell books at below-market prices is to get the books at a discount from ...

Samir-Ghani July 1, 2019

Is it because of the Either that appears right after?

Meredith August 13, 2019

@Mehran When was it stated that must introduces a necessary condition? I don't have it in my notes and see it was asked on this message board but without a response. I too was confused on how to diagram the last sentence since "either or" was present yet I recognized it was not in a traditional set up but had no clue what my option was for diagramming until seeing the video.

Ravi August 13, 2019

@Samir-Ghani and @Meredith,

Happy to help.

The word "must" introduces the necessary condition. Think about it;
what does "must" mean?

It means "be required to" or "need to," so it means that whatever
follows has to occur. This is why it introduces the necessary
condition.

Here's how we diagram the stimulus:

Profitably Sell - >Discount.
No High Volume - >No Discount.
High Volume - >Cater to Mass Tastes OR Specialized Market Access

Looking at the prompt, we're told an additional fact—the bookstore
doesn't cater to mass tastes. Using this, we're asked to choose the
answer that must be false.

We can link our conditional statements up to make a chain.

Profitably Sell - >Discount - >High Volume - >Specialized Market Access
or Cater to Mass Tastes

Since the stem tells us that the bookstore doesn't cater to mass
tastes, then we can modify the chain to look like

Profitably Sell - >Discount - >High Volume - >Specialized Market Access

The correct answer choice will be something that contradicts this
chain since this is a must be false question. The chain can be
violated by affirming a sufficient condition while denying a necessary
condition. Let's look for a contradiction in the answer choices.

(D) says, "The bookstore does not have exclusive access to a large
specialized market but profitably sells some of its books at
below-market prices."

(D) contradicts the chain we made because it denies a necessary
condition (the bookstore doesn't have exclusive access) while
satisfying a sufficient condition (the bookstore profitably sells).
Thus, (D) is the correct answer choice.

Does this make sense? Let us know if you have any other questions!