Fact #1: Each of the 200 participants attended "at least 1 two-hour concert of classical music per week" over the 12 week semester. Thus, each participant, at a minimum, viewed 12 concerts (or 24 hours of concert time, since each concert was two hours long).
Fact #2: Ten students attended "the greatest number of concerts." Thus, these students must have attended more than the minimum 12 concerts.
Fact #3: The 10 students from fact #2 reported "lower stress levels and higher satisfaction with their lives." However, we are not offered a comparison group, so we don't know with whom these students are being compared.
Fact #4: Twenty students attended the "fewest number of concerts." This indicates that there must be at least three levels of concert goers: "Fewest" = 20 students (fact #4), "Greatest" = 10 students (fact #2), and "the rest" = 170 students (fact #1)
Fact #5: Most of the 20 students from fact #4 reported "below-average levels of emotional comfort." However, we don't know how many "most" equals, and we aren't certain whether "emotional comfort" is equivalent to "lower stress levels and higher satisfaction with their lives."
Now, let's look at the answers
(A) Most of the 200 participants improved their emotional state and lowered their stress levels. We have no information about "most of the 200 participants." All we know (from fact #3) is that the ten students who attended the greatest number of concerts reported "lower stress levels and higher satisfaction with their lives."
(B) During each week of the experiment, the participants spent at least 2 hours less on their academic work as a result of concert attendance. No information about academic work is offered in the argument.
(C) Listening to classical music for at least 2 hours per week improves the emotional well-being of the majority of young adults. This is a typical GMAT "attractive distractor" (i.e. an incorrect answer choice the test makers intentionally make attractive.) However, this answer has several faults. First, we have no idea how the "majority" of our concert-goers reacted to the study; we are only given minimal information about 30 of the concert-goers. If we can't even make claims about the majority of concert-goers in the study, how can we make claims about "the majority of young adults." Second, all of our concert-goers in the study listened to classical music for "at least 2 hours per week" (at least for the duration of the study). From those participants that we know about, some reported negative emotional states and some reported postive emotional states. This contradicts the contention that listening to classical music "for at least 2 hours per week" improves emotional well-being.
There are several other problems with this answer, but I want to address this specific answer type more broadly. In general, the GMAT likes to provide a CORRELATION in a text and then claim CAUSATION in an answer choice. This is extremely common on inference/draw a conclusion critical reasoning arguments, and the causal answer choices are almost always incorrect. If you choose an answer choice that claims causation, you MUST be able to prove this causation from the text of the argument.
(D) More than 6 participants attended at least 14 concerts during the course of the experiment. Our facts have proved that there are at least three levels of concert goers: fewest (20 students), greatest (10 students) and "the rest" (170 students). The fewest attended at least 12 concerts (by definition of the study); thus, "the rest" must have attended at least 13 concerts and "the greatest" must have attended at least 14 concerts. Since "the greatest" includes 10 students, it is true that More than 6 participants attended at least 14 concerts during the course of the experiment.
(E) At least some of the students participated in the study in order to gain free access to classical concerts. We are given no information over the motivations of the students.
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