Scientists have discovered a new species of butterfly that lives only

Question

Scientists have discovered a new species of butterfly that lives only in a small region of Central America and is active only at night. During the day, it rests in treetops, where its green color matches the foliage perfectly. Therefore, the scientists must have discovered the butterfly at night.

The argument depends on which of the following assumptions?

A) The newly discovered butterfly is not related to any other species of butterfly.
B) There is no way for the scientists to detect the butterfly during the day.
C) No other butterfly species lives in this region of Central America.
D) The foliage in the butterfly's habitat is completely green.
E) The butterfly cannot survive in areas outside of Central America.

Bunuel · Answer

OFFICIAL EXPLANATION

The correct answer is B.

The conclusion of the argument is that "the scientists must have discovered the butterfly at night." Why? Because the butterfly's color matches the green of the foliage, and the butterfly is active only at night. In order for this argument to work, one has to assume that there is no way for the scientists to detect the butterfly during the day, despite its camouflage. If there is a way for the scientists to detect the butterfly during the day, the conclusion is no longer logical.

carlton17 · Answer

Thanks for the explanation  Bunuel .
Referring to option D, the fact that the foliage in the butterfly's habitat is not completely green directly contradicts the premise in the argument. With this statement added to the argument, the conclusion is no longer logical as well. However, on the GMAT, should we avoid accepting answer choices (especially in weaken/ assumption questions) that contradict a premise?

PyjamaScientist · Answer

Hi  carlton17 ,
Though it's often said that the "premise" should be taken as it is provided. I have seen cases where breaking the logicality of the premise too has proven to be the correct answer. So, rather than memorising what can be challenged and what can not be challenged, if one focuses on the argument as a whole, with special attention to the conclusion, one would not need to memorise anything.

This choice brings in information with respect to the foliage on which the butterfly rests. (D) says that the foliage is entirely green. You wrote above: 
 I think you have written a "negated version" of (D). And does the negated version really "contradict" the conclusion that "the scientists must have discovered the butterfly at night"? Maybe there were spaces in the foliage like stems/barks/vines that were not entirely green. But what if these things make up a very small percentage of the foliage? In that case, our conclusion would hold. Compared to negated version (B), "if there is a way for the scientists to detect the butterfly at day", then the conclusion "the scientists must have discovered the butterfly at night" breaks down completely.

Advice: I am not a big fan of the "negation technique" in Assumption type questions. When this works, it works, but I have seen it confusing test takers when applied blindly. A better technique is to not approach CR with a set of formulas. Understand the stimulus as it is presented. Look for logical fallacies or the "jumps" that the author might have taken to reach his/her conclusion. And then use POE to eliminate answer choices.

carlton17 · Answer

Thanks a lot. Much appreciated.

ajinkyajadhav · Answer

A,C,E are completely first time eliminate and thus no need to reassure the same,
between B and D some people might find it tricky but it asks for how would they be discovered at night and hence you sufficiently point of the option of not in the day and hence B is clear easy winner.

notcoolDwight · Answer

I think option D holds true as much as option A. The Scientists would not have discovered the butterfly if not for the assumption that the foliage was all green.

AbhishekP220108 · Answer

Hi  notcoolDwight  , "the foliage was all green" is not an assumption. The conclusion is that  "the scientists must have discovered the butterfly at night."

The premise he used to arrive at conclusion for a newly discovered butterfly is that it lives only in a small region of Central America and is active only at night. During the day, it rests in treetops, where its green color matches the foliage perfectly.

For the conclusion to be true, we have to find something that, if negated, breaks the conclusion.

What would a scientist be thinking? Is it possible that there are no other means to detect the butterfly during the day? If there is a means to detect it, then the conclusion will not hold. Option B clearly brings that necessary condition. As per option A, we are not worried about other species. Also, option D says the foliage is all green, which is already given; all green or not all green, we are concerned, even though it is all green butterfly foliage.

Scientists have discovered a new species of butterfly that lives only

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Scientists have discovered a new species of butterfly that lives only

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