uwhusky - please join us! I just figured your invitation was implied...
Here's the deal with "some" - the only thing that it truly means as far as GMAT logic is "not none". It could mean anything from 1 to all, inclusive.
Let's say I said this. Based on my message board activities, I'd say that uwhusky and paes want to do really well on the GMAT. So I could say "some people posting on this thread would like to do well on the GMAT". And I'm right.
Well, I think that all of us want to do really well on the GMAT. But I'm not wrong in saying "some" - maybe I didn't do enough research to be able to say "all", so I just said "some". "Some" doesn't mean that "all" or "most" are not true.
So...be careful with those percentage estimates of when to use some/most/etc. "Some" includes everything but "none".
As for this question, "some people who know how the government works don't know how it was formed" introduces doubt in the conclusion.
Think about it this way - you're at a school board meeting and the item up for vote is, essentially, "to make sure that people know how the government works we should teach them how it was formed". You want to weaken that conclusion because you think it's a waste of money. Yeah, it would be terrific if you could prove that most people who know government don't know its history, but if all you have are two members of the City Council that you can use as evidence, that still introduces doubt:
You: "Mr. Mayor, Ms. Controller, do you know how our government was formed?"
Response: "No, quite honestly we don't."
You: "Ladies and gentlemen, some people who clearly understand how government works do not know at all how it was formed. Therefore it's not necessary for us to invest in a program to teach students how the government was formed, and we can spend the money in a better way!"
Your job in a weaken question is to introduce doubt, or to emphasize that logical flaw between the premise and the conclusion. If you use choice B, it's enough to introduce that doubt that the premise does not guarantee the conclusion.
One more point, paes - to your point that "based on the majority, we should teach government history", we don't know that anyone, let alone the majority, who knows government history knows how it works. All we know is that some people who do know how it works (based on B) do not know its history. That's more LSAT-style logic (I suspect that's where this problem was adapted from), but could be helpful to know.
Brian Galvin
GMAT Instructor
Chief Academic Officer
Veritas Prep
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