Formal logic help please

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Joined: Wed Oct 20, 2010 8:47 pm

Formal logic help please

Postby sighsigh » Wed May 08, 2013 5:29 pm

I am having a horrible time trying to understand PT#57, S#3 (LR2), Q#17. This is an abstracted, somewhat simplified version of the stimulus:

(A + B + C) => D

What are the assumptions that are necessary and together sufficient? I am thinking they are:
(B + C) => D

Is this correct? The former assumption is confirmed by the correct answer choice to Q#17, which is (D), but I am unsure about the latter assumption.

Posts: 101
Joined: Sat Feb 09, 2013 5:04 pm

Re: Formal logic help please

Postby Trajectory » Thu May 09, 2013 10:17 am

No pro at this but I'll give it a try.

I think at its basic, in abstract terms, the stimulus says:

A (bought watch there) & B (used only as intended to be) & C (stops working next day) ----> D (refund)

From there it goes to conclude that A & C so then D.

Buts its missing B (assuming that it was used in the only way it was intended to be)....Answer choice D. If negated the conclusion wouldn't work. If you negate we would have A+(~B)+C--->D. How could that be when the stimulus says A+B+C--->D?? You need all 3 for a refund. Not 2 out of 3.

Posts: 263
Joined: Wed Oct 20, 2010 8:47 pm

Re: Formal logic help please

Postby sighsigh » Fri May 10, 2013 9:39 am

Thanks for the response, Trajectory. Your analysis of the argument you described in your post is correct. However, that argument isn't quite what the stimulus is saying. You missed the jump between 'department store' and 'non-department store.'

Watch bought at department store + used properly + stops working next day => department store refund
Watch bought at non-department store
stops working next day
non-department store refund

One necessary assumption is "used properly," which is what the correct answer choice, (D), states. I am wondering what other necessary assumptions you would need to justify this conclusion.

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