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#26 - All known deposits of the mineral tanzanite are in

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Complete Question Explanation

Parallel Reasoning-SN. The correct answer choice is (D)

The argument in the stimulus can be summarized as follows:

    Premise: ..... Tanzanite stones ..... :arrow: ..... Tanzania

    Premise: ..... Ashley collection ..... :arrow: ..... Tanzanite stones

    Conclusion: ..... Ashley collection ..... :arrow: ..... Tanzania

(i.e. she is unlikely to collect stones not originally from Tanzania)

Use the conclusion test to eliminate answer choices (B) and (E), and the premise test to eliminate (A). The real contenders should only be answer choices (C) and (D).

Answer choice (A): The premise test can be used to quickly eliminate this answer choice. We need a premise of the type "All A's are B" (all tanzanite stones are in Tanzania), not "Many A's are B" (the lagoon on Scrag Island is home to many frogs). This answer choice is incorrect.

Answer choice (B): The conclusion test eliminates this answer choice. Ashley is unlikely to ever collect a stone not originally from Tanzania. Here, the owls may never ear an animal that lives outside the lagoon. Furthermore, answer choice (B) does not suggest that the owls on the island eat only Scrag Island frogs. Rather, it is that the frogs on the island are eaten only by Scrag Island owls. It is perfectly possible that the owls may eat other animals as well. The conclusion in answer choice (B) is similar to a Mistaken Reversal of the one needed.

Answer choice (C): At first glance, this is an attractive answer choice, since the second premise and the conclusion match the stimulus precisely:

    Premise (2): ..... Owl diet ..... :arrow: ..... Island frogs (owls eat only island frogs)

    Conclusion: ..... Owl diet ..... :arrow: ..... Lagoon (owls eat only lagoon animals)
For the conclusion to be true, the first premise needs to state that:

    Island frogs ..... :arrow: ..... Lagoon (i.e. that all island frogs live in the lagoon)

However, this is not the idea presented here. If frogs are the only animals known to live in the lagoon, this does not mean that they don't live elsewhere on the island: it only means that no other animals live in the lagoon. If frogs lived elsewhere on the island, the owls may be eating frogs other than the ones found in the lagoon. In short, the first sentence of this answer choice is the Mistaken Reversal of the one we need.

Answer choice (D): This is the correct answer choice:

    Premise (1): Island frogs ..... :arrow: ..... Lagoon (the only frogs live in the lagoon)

    Premise (2): Owl diet ..... :arrow: ..... Island frogs (owls eat only island frogs)

    Conclusion: Owl diet ..... :arrow: ..... Lagoon (they eat only lagoon animals)

The only difference between answer choice (D) and (C) is in the first premise.

Answer choice (E): The conclusion test can be used to quickly eliminate this answer choice, since the certainty of "no owl will eat anything that lives outside the lagoon" does not parallel the probability that Ashley is unlikely to collect a stone not originally from Tanzania. This answer choice is incorrect.
netherlands
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Hi there PS, I was working in the Chapter 8 homework, Number 15, in the Parallel Reasoning Section!, and was confused about how the conclusion test eliminated answer choice B. Do "may never" and "unlikely to ever" not mean the same thing?

Unlikely to ever - Unlikely it'll happen
May Never- Possible it will never happen ... or It is unallowed and unable to happen?

Thank you!
Nikki Siclunov
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"May never" and "unlikely to ever" are similar enough to make me hesitant to eliminate answer choice (B) on that basis alone. The reason why (B) is wrong is because it fails the Premise Test. We are looking for premises that establish the following chain:

    Premises: Collect :arrow: Tanzanite stones :arrow: from Tanzania

    Concl.: NOT from Tanzania :arrow: NOT collect (unlikely to ever)

With (B), we have two necessary conditions for the same sufficient condition:

Frogs on Scrag :arrow: Lagoon
Frogs on Scrag :arrow: Eaten by Scrag owls

I wouldn't have even looked at the conclusion: after reading the premises, I would have crossed off (B) and moved on.
Nikki Siclunov
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GLMDYP
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Hi!
For this question, I feel all the five choices are the same!! Help me solve this question please.
Thanks!
I put my trust in your guys! ;)
Lucas Moreau
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Hello, GLMDYP,

For Parallel questions, it can be helpful to not just diagram the stimuli, but to replace the diagram components with placeholder letters, to get a sense of the abstract nature of the logic. For example, if I wanted to say that eating healthy led to higher life expectancy, and higher life expectancy led to greater quality of life, I could diagram that like this:

Eating healthy :arrow: Higher life expectancy :arrow: Greater quality of life

And I could then replace the bits of the diagram with generic letters. Like so:

A :arrow: B :arrow: C

That is the basic structure of the logic of those two statements. The structure is the same if I were to say...hmm, studying more for the LSAT will lead to a better score, and a better score will lead to greater prospects for law school.

Studying more for the LSAT :arrow: Better score :arrow: Greater prospects for law school

A :arrow: B :arrow: C

So I told you that story to tell you this story. ;) That is, in this question, the stimulus could be diagrammed as follows:

If there is a deposit of tanzanite [from which any tanzanite stone would be obtained], then it was most likely [to account for unknown deposits] from Tanzania.
If Ashley collects a stone, it is a tanzanite stone.
Conclusion: Ashley is unlikely to collect any stone not from Tanzania.

And that can be reduced to its basic structure as follows:

If there is an Object A, then it was most likely from Place B.
If Person C obtains an object, it is an Object A.
Conclusion: Person C is unlikely to obtain any object not from Place B.

Now, looking at the correct answer choice D, we get:

If there is a frog on Scrag Island, then it was most likely from the lagoon.
If an owl on Scrag Island eats an animal, it is a frog on Scrag Island.
Conclusion: An owl on Scrag Island is unlikely to eat any animal not from the lagoon.

Which also reduces to the same structure immediately above, though it's an owl instead of a person. Good enough for these purposes. :-D

Sorry if that was a little long-winded, and be sure to ask if you have any follow-up questions.

Hope that helps,
Lucas Moreau
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Kp13
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Hi,

I was confused about how to diagram the answer choices correctly to this problem.

Especially confusing for me are statements like: "No owl on Scrag Island is known to eat anything but frogs on the island." Would that be the same as: "Every owl on Scrag Island is known to eat nothing but frogs on the Island?"

i.e: All owls eat only frogs on the island (Owl :arrow: Frogs on Island).

I am having a hard time understanding why choice E is wrong?

Thank you,
Adam Tyson
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KP,

Your diagram of that statement looks pretty good to me, except for one missing element, and that's the "known" element. The statements aren't absolute - it's not that the owls don't eat anything else, just that they aren't known to eat anything else (just like the stimulus says the only known tanzanite is from Tanzania, rather than the more extreme claim that all tanzanite IS from Tanzania). Be sure to include that "known" element - something like "Owl on Scrag Island --> known to eat stuff other than frogs from the island.

Check out the conclusion in answer E and notice how absolute it is. Our stimulus talked about probability, not certainty, by using the word "unlikely." The conclusion in E leaves out any uncertainty/probability and goes all the way to saying no owl will eat anything else but those frogs. If the conclusions aren't parallel in their use or force of language, then the arguments aren't parallel. Look instead for an answer that retains that element of probability rather than certainty.
Adam M. Tyson
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forloop
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Hi,

I'm having a bit of trouble understanding the homework explanations for this problem? Specifically, answer choice B? I see how D is the right answer, but I wasn't sure how to eliminate B from the conclusion matching test? For the stimulus, the conclusion said that "she is unlikely ever to collect a stone not originally from Tanzania", whereas the conclusion for B says "hence the owls may never eat an animal that lives outside the lagoon."

I thought unlikely and may both described possibilities?

Thanks!
Nikki Siclunov
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Hi forloop,

Thanks for the question. "Unlikely to ever" does not denote the same level of probability as "may never." I know, I know... they do sound similar, and the nuance is very subtle. But it's there. Let me explain:

If I told you that "I may never become a rock star," I am not telling you how likely it is that I will become one. I am only suggesting that there is a real possibility of me not becoming a rock star. In this context, the following words give no indication as to the likelihood of an event's occurrence: they only indicate a possibility that the event may (or, respectively, may not) occur:

Possibility

    can
    could
    may
    might
    possibly
    some
    at least one

If I told you, however, that "I am unlikely to ever become a rock star," I am a lot more pessimistic about my chances. "Unlikely to ever" communicates an (almost) virtual certainty that the rock star thing ain't happening. It suggests a very high probability of non-occurrence, which is different from the one suggested in answer choice (B). Indeed, the following words designate a higher (or, in the negative, a lower) level of probability than the words listed above:

Probability

    Likely (or unlikely)
    Probably
    Tends to
    Usually
    Most

Since the probability level in the conclusion of answer choice (B) differs from that in the stimulus, answer choice (B) is incorrect. You should also notice that (B) contains faulty logic. The second premise tells us that "the frogs on the island are eaten only by the owls on the island," not that the "owls on the island eat only the frogs on the island." See the difference? The premises in answer choice (B) leave open the possibility that the owls also eat lizards, snakes, etc., so they may well be eating animals that live outside the lagoon.

Does this make sense? Let me know.

Thanks!
Nikki Siclunov
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z.em
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Hello,

I did this question twice, and chose the same wrong answer--C.
I read the explanation and diagram below; however, I have C and D diagramed nearly identical:
Answer C: Frog--> Lagoons [ Frogs are the only animals known to live in lagoon]
Owl--> Frog [Owl diet consists nothing but frog]
Owl--> eat animals in Lagoon [Owl unlikely to eat animal outside of lagoon]
I diagramed Answer choice D in the same exact manner. Can you please explain what I missed in answer choice C, that makes it wrong.
Thank you!