pt63 s1 q23 - flaw question. please help!

dlrbfl
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Joined: Mon Sep 09, 2013 12:23 am

pt63 s1 q23 - flaw question. please help!

Postby dlrbfl » Fri Sep 13, 2013 2:44 am

This is a flaw question and I thought the flaw was mistaken reversal.


Stim:

Certain makes of car are more common in some regions of the nation than in other regions -> lead many ppl to overestimate
This is precisely the result found in the experiment.

Thus, certain makes of car are in fact more common in some regions of the nation than in other regions.

(X-> Y
Y ->X)

Then I tried to find an answer choice that points out this flaw, but couldn't find one.
I eliminated B because of the word "support," reasoning that the presence of Y doesn't support the existence of X. (It's mistaken reversal)

What am I missing here?

Any help would be greatly appreciated. Thanks!

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Silvermanlsat
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Re: pt63 s1 q23 - flaw question. please help!

Postby Silvermanlsat » Fri Sep 13, 2013 12:41 pm

This is kind of a unique question in that it's not a common flaw seen too often on the LSAT. Viewed as a conditional statement, however, it is quite similar to other questions.

We're told that there is an hypothesis. The hypothesis can be viewed as a conditional statement.

If certain makes of cars are more common in some regions than in other regions, then many people will overestimate how common their car is nationally.

Keep in mind that certain makes of cars being more common is some regions than in others is merely a sufficient condition for people overestimating their cars nationally. It is not a necessary condition, so learning that people overestimate how common their cars are nationally does not provide us with a valid conclusion that certain makes are more common in some regions than in others. There could very well be other reasons why people will overestimate how common their cars are nationally that has nothing to do with how common cars are regionally.

But we are then told that because we learned that many people overestimate how common their cars are nationally (the necessary condition in the conditional statement above), we can conclude that certain makes of cars are more common in some regions than in others (the sufficient condition in the conditional statement above). Proving the necessary condition does in fact support the hypotheses, but it does not prove the hypothesis (because, again, something else might have caused the result). As such, choice B is correct.

Symbolically, if we have A->B, and we learn that B is true, we can't conclude anything about A. Only if we learn that B is not true can we then conclude that A is not true.

bp shinners
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Re: pt63 s1 q23 - flaw question. please help!

Postby bp shinners » Fri Sep 13, 2013 1:25 pm

Silvermanlsat wrote:Symbolically, if we have A->B, and we learn that B is true, we can't conclude anything about A. Only if we learn that B is not true can we then conclude that A is not true.


Well, we can conclude that A might be true. I only bring it up because the LSAT has used that trick a few times recently.

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Silvermanlsat
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Re: pt63 s1 q23 - flaw question. please help!

Postby Silvermanlsat » Fri Sep 13, 2013 3:59 pm

Very good point. I suppose what I meant is that we can't conclude that A must be true or must be false given that B is true.




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