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#10 - All of John's friends say they know someone who has

Dave Killoran
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Complete Question Explanation

The correct answer choice is (E)

The fact set in this stimulus is fairly compact, and includes the following two premises:


    1. All John's friends say they know someone who has smoked 40 cigarettes a day for the past 40 years but is fit and well, and;

    2. John doesn't know anyone like that and is sure that at least one of his friends doesn't know anyone like that either.

The question stem is a Must Be True, and thus we know the statements above are 100% true. If this is the case, we initially have a conflict because all of John's claim to know a heavy smoker who is quite fit but John says he doesn't, and that he's not unique among his friends. So, someone isn't telling the truth here. However, we actually can determine that it is john who is telling the truth because the stimulus states that "it is quite certain" that John is not unique. So, the stimulus notes that his friends "say" they know someone, but that John definitely does not know anyone like that and it is a fact that he is not alone in that. So at least one of John's friends is not telling the truth. Answer choice (E) states this directly and is correct, but let's review each answer to see why they are incorrect.


Answer choice (A): Smokers may often lie about how much they smoke, but it doesn't matter unless we know that the smokers John's friends know are lying about how much they smoke. John's friends could know only honest smokers that are telling them the truth. So this answer choice is incorrect.

Answer choice (B): Similar to answer choice (A), this is a general statement that doesn't affect or follow from John's friends or the supposed smokers that they know. The statements made by his friends, and the factual circumstances of what we know about John (as explained below in more detail in answer choice (E)) make it so that it is irrelevant whether people knowingly exaggerate. And in any event, we cannot know for sure that what occurred in the stimulus involves "knowingly exaggerat[ing] without intending to lie" —there's no proof of that occurring.

Answer choice (C): This answer choice could be true, but it does not have to be true. Since this is a Must Be True question, this answer is then incorrect.

Answer choice (D): This answer choice goes too far in saying "most." While we know at least one of his friends isn't telling the truth, we don't know that "most" of them aren't telling the truth, and thus this answer choice is incorrect. Another reason this answer cannot be correct is that if you select it as true, you automatically also force answer choice (E) to be true (since "most" automatically implies "some). Since you cannot have two correct answers to a problem, this answer is incorrect on that basis alone.

Answer choice (E): In LSAT terms, "some" means "at least one" or more, or anywhere between 1-100%. According to the stimulus, John is not alone in not knowing a smoker who fits the description in the stimulus, and so at least one of his friends (and thus "some" of his friends), must not be telling the truth.

Note that it can be difficult to pick answer choice (E) because it feels so powerful and definitive. It feels very strong (and it is), but that's acceptable because the stimulus has been very clear that John's situation is factual. Since his friends statements counter his, it has to be that at least one of them is not telling the truth.

If the "not telling the truth" aspect bothers you here, think about it this way: each of his friends was asked if they know a heavy smoker who was still fit. They each said yes. However, we know that John knows no one like this, and we also know that he's not the only one of his group who doesn't know a heavy smoker who was still fit. Thus, someone who said they know this smoker actually doesn't. Therefore, in saying they did, they lied.
Dave Killoran
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reop6780
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The only inference that I can make based upon, "he is not unique among his friends in this respect" is that his friends do not know the guy smoking and fit at the same time.

Basically, I cannot distinguish the answer D from E.

Where does the difference of "most" and "some" come from?

Thank you

Hyun Kim
David Boyle
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reop6780 wrote:On the page 29, question number 30, the answer is E.

The only inference that I can make based upon, "he is not unique among his friends in this respect" is that his friends do not know the guy smoking and fit at the same time.

Basically, I cannot distinguish the answer D from E.

Where does the difference of "most" and "some" come from?

Thank you

Hyun Kim


Dear Hyun:

Well, how many of his friends are not telling the truth? "Some" could mean only 1. John is "not unique" among his friends, which only means that at least one must also not know somebody who's smoking and fit. Therefore, John could have 200 friends, and maybe 199 of them know someone who smokes and is fit. Then, John and just one other friend could not know someone like that, and John would still be "not unique". So E, with "some" not "most", is correct.

David
reop6780
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Wow, that is the easiest way to distinguish between "some," and "most" !

Thank you

Hyun Kim
Dave Killoran
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Hi Hyun,

Good question! You have the LSAT Logical Reasoning Bible, correct? Go to Chapter 11 and look at the section titled: Formal Logic Relationship Indicators Defined Numerically. Those two are discussed there.

Please let me know if that helps out. Thanks!

Edit: I thought your reply said "what," not "that," so my answer may not be what you were looking for. I'll leave it in case anyone else is looking for this info :-D
Dave Killoran
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180nce
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The question is: All of John's friends say they know someone who has smoked 40 cigarettes....

I was between d and e but ended up picking d using the following reasoning: unique is equal to some number that is less than half, so if John has 10 friends and 9 of them are lying, he is not unique among them for not knowing a fit smoker because only 1 person in the group of 11 friends actually knows the smoker.

Can someone please let me know where I faltered. I am guessing it is in my understanding of the word "unique"

Thanks!
Jon Denning
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Hey 180,

Thanks for the question! I think you're mostly on the right track here, and probably correct that any confusion arose from the use of "unique." All it means to not be unique is that there is at least one other person like you, or in this case at least one friend, like John, who doesn't actually know anyone who's smoked 40 cigarettes a day for 40 years and is still healthy.

What that means then, is that if all of his friends claim to know someone like that, and at least one of them actually doesn't (since John isn't unique in not knowing anyone like that), then at least one friend must be lying. On the LSAT "at least one" is identical to "some," which proves (E) right.

Further, think about what picking (D) would mean: if most of his friends are lying, then it would in fact prove that at least one (some) of his friends is lying, and (E) would be true by default. Literally picking (D) makes (E) true, which is something that can never happen with a correct answer choice on the LSAT.

I hope that helps!
Jon Denning
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mrcheese
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I understand that the stimulus says it is "quite certain" that John is not unique, but it feels like it is a jump to make the conclusion that one of John's friends is definitely a liar. They must be a liar? If something else "could" be true then it seems like that could inherently hurt the MBT answer in this situation... I can see that the stimulus says "all" of John's friends say this about smokers and fitness and it does seem strange. I would say it is probable that one could be lying but probable does not mean it is impossible. I can flip a quarter and land it on heads 1,000 times and it is not impossible, it just isn't probable. Do the other answers not fulfill the "quite certain" requirement?
mrcheese
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I feel like E "could" be true, but that is it. Maybe it is just the best answer?
Robert Carroll
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mrcheese,

"It is quite certain" entails that it is true. So John is not the only person who knows no one who has smoked and is fit. But all his friends say the opposite. So at least one of his friends is saying something that is not true. That is what answer choice (E) says.

Robert Carroll