PT 61 S2 Q23

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PT 61 S2 Q23

Postby niederbomb » Wed Dec 08, 2010 9:51 am

I got this one right, but during review, my head hurt, and I wondered how I actually got it right.

The answer is D, but A looks pretty good too. What is the best way to attack this question?

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Re: PT 61 S2 Q23

Postby AverageTutoring » Wed Dec 08, 2010 2:15 pm

Forgive me if this is the wrong question but I am working out of the disclosure booklet and not the released test. It's the first LR section, yes? The question about the brick houses?


Brick House on River Street --> Front Yard

Most Front Yard --> Two Stories


Most Brick Houses --> Two stories


If you are a brick house you have a front yard, and most of the houses that have front yards have two stories. But does that necessary mean that most of the brick houses have two stories? Not necessarily.

Consider an example, say there are 10 brick houses on the street and 100 houses in total (so 90 non brick houses). For arguments sake lets say every house has a front yard. But lets also say that all 90 non-brick houses have two stories and none of the 10 brick houses have two stories. Does this satisfy the stimulus? Absolutely. Because the stimulus only says that most houses (in general, so brick and non brick alike) with front lawns have two stories which we satisfy when we say that the 90 non-brick houses have two stories. But we also said that no brick house had two stories, so the conclusion that most brick houses have two stories is clearly unwarranted in this example even though we satisfied the conditions in the stimulus.


A: This answer is wrong because it switches up the necessary/sufficient conditions. We can certainly draw this bad boy out.

L--> P

Most L --> RO

Most P --> RO

The flaw here is that just because all legislators are politicians and that most legislators run for office, that doesnt mean most politicians have run for office. What if the vast majority of politicians are not legislators and come from some other group?

If we diagram the original stimulus,

BH --> FL

Most Houses with FL --> Two Stories

Most BH --> Two Stories

Notice how the second conditional statement plays off the necessary condition of the first? Whereas in the answer choice, the second conditional statement uses the original sufficient condition again? Also, the conclusion in the answer choice plays off the necessary condition of the first statement whereas the conclusion in the stimulus plays off the sufficient condition in the stimulus.

D on the other hand,

L --> PS

Most PS --> Never RO

Most L --> Never RO

Like the stimulus the second conditional statement plays off the necessary condition from the first statement. And the conclusion follows.

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Re: PT 61 S2 Q23

Postby niederbomb » Wed Dec 08, 2010 7:52 pm

Thanks for explaining that. It makes more sense now. One way I've answered some other similar questions is by drawing circles inside each other. I wonder if that's a good approach.

For example, brick houses could be the smaller circle within houses while legislators is a smaller circle inside public servants.

So, I guess choice A generalizes from small circle (legislator) to big circle (politicians) while the stimulus generalizes from big circle (public servants) to small circle (legislators).

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