PrepTest 24 - Dec `97 - Q 19

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PrepTest 24 - Dec `97 - Q 19

Postby law_girl1 » Tue Sep 20, 2011 3:19 pm

I need some help on this question, I`m confused as heck on how to diagram it, and two answers come out correct..
This is the way I did it..


some PT --> not WS

not HL --> PT --> not WS

so the contra is WS --> not PT --> HL

which means both A and D could be correct... help please! also any tips for such every/some ques? Thanks

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Re: PrepTest 24 - Dec `97 - Q 19

Postby chrisbru » Tue Sep 20, 2011 4:29 pm

Try looking here, it may help. I'd try to help, but can't find this preptest to look at the question. ... g-f51.html

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Re: PrepTest 24 - Dec `97 - Q 19

Postby timmydoeslsat » Tue Sep 20, 2011 7:57 pm

We can diagram the stimulus like this:

Student who walks to school ---> Goes home for lunch
PTJ some ~Walk to school

The premise is above the line, the conclusion of the argument is beneath the line.

This question asks us for an assumption (unstated premise) that we can plug into the argument to make the conclusion follow validly.

I see that PTJ is not mentioned in the premise. This must be addressed in some manner in the premises for us to be able to conclude something about it.

I also notice that we have ~Walk to school in the conclusion.

We can arrive at that variable if we enact the contrapositive of the premise given, such that we arrive at this conditional now:

~Go home for lunch ---> ~Student does not walk to school

So I know that if we are given something about PTJ and ~go home for lunch, we can validly derive the conclusion of ~Student does not walk to school.

Answer choices:

A) ~PTJ will not get us anywhere. We want something with PTJ as the variable. Plus, you cannot take contrapositives of some statements (or most statements for that matter). So eliminate this one.

B) This says: Student goes home for lunch ---> PTJ. This will not give us ~Walk to school. Eliminate.

C) Again, ~PTJ, this will not work.

D) PTJ some ~Go home for lunch. We know, via the contrapositive of the premise given in the stimulus, that every student that ~Go home for lunch, does ~walk to school. This would give us PTJ some ~Walk to school.

E) Does not even contain the variable PTJ.

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