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Dogs

by crackthetest » Sun Oct 18, 2009 5:35 pm
Most large dogs are gentle, but most large dogs scare people. In addition, all dogs who scare people are reliable protectors.

Which can be logically concluded from above?

a) Most dogs that are reliable protectors are gentle.
b) Some gentle dogs are reliable protectors.
c) All dogs that are reliable protectors are large dogs.
d) Some dogs that are not gentle scare people.
e) All large dogs are reliable protectors.

Can you let me know the reason behind your answer choice. OA will follow.
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by ershovici » Mon Oct 19, 2009 7:07 am
IMO B
A - we don't know what proportion of dogs that are reliable protectors are gentle.
B - we know that a portion of relaible protectors are large dogs, and most of them are gentle
C - not all but most large dogs are protectors
D - we don't know about small dogs, wether they are gentle and scary people
E - the same as C
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by delhiboy1979 » Tue Oct 20, 2009 2:31 am
I think it is A.
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by Testluv » Tue Oct 20, 2009 6:56 am
The answer must be B. When you have two majoritys overlapping (two "mosts"), there is always at least one object that has those two traits. Here, this mean that there is at least one (ie, some) large dogs that are both gentle and scare people. The second sentence tells us all scary dogs are reliable protectors. Therefore, there must be some large, gentle, scary dogs that are reliable protectors. While B is under-comprehensive (ie, it does not say everything that we know must be true), it still must be true given the above deduction.

In inference questions, you should look for duplicated terms, arrive at a deduction, and aggressively scan the answer choices for a choice that matches your deduction.
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by Testluv » Tue Oct 20, 2009 8:51 pm
Hi crackthetest,

I hope that helps answer your question.

I should add that this does not at all sound like a question that would actually show up on the GMAT. While there is only one truly and demonstrably correct answer, this sounds way more like a mock LSAT question, one that is trying to test LSAT subtleties of formal logic conventions (some vs all; negating/reversing, etc.) In the OG, the test-maker explicitly states that the GMAT CR section does NOT test "formal logic conventions." And, have you ever seen a question like this in the OG?

My advice is to be careful to study only GMAT questions and, if you need extra practice, questions from a legitimate source (major test prep company).
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by Ludacrispat26 » Tue Oct 20, 2009 9:06 pm
lol, this is a sample problem in PowerScore's Free CR Bible Chapter (page 14):

https://powerscore.com/newmedia/GMAT-Cri ... pter-2.pdf

OA is B
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by Testluv » Tue Oct 20, 2009 10:24 pm
Hi Ludacrispat26,

I would respond that just because it is called a "bible" does not make it the gospel truth!
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ans

by crackthetest » Wed Oct 21, 2009 5:05 pm
Yes that was from a GMAT source as stated above.

and OA is B. Though I have to agree I haven't seen such a question in any other GMAT books I referred, this question stood at me. I'm trying to think if this can be worked through logical comparison. ( ex: A -> ~B )
but since it has most/some/all I couldn't arrive at such scenarios and wondered if I could bounce this with some here. Thanks for all your explanations.
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by Testluv » Wed Oct 21, 2009 7:09 pm
To be clear, what is meant by official GMAT source is questions from the actual test-maker, such as those that come from the OG, and those that come from the official GMAT Prep tests. Because Powerscore is not the test-maker, it is not a "GMAT source". Instead, it is a GMAT-like source.
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