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Fifteen college seniors, none of whom took any math classes [#permalink]
11 Oct 2017, 22:12

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Difficulty:

5% (low)

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0% (00:00) wrong based on 0 sessions

Fifteen college seniors, none of whom took any math classes in college, were selected for a clinical trial. An online GRE Math Course was made available to them, and these students were allowed to study for however many hours they wanted. Then, each took the GRE for their first time. The graph below records how many hours each student studied, using the online material, and that student’s GRE Quant score. The best-fit line model shows the best prediction, given such a student’s hours of study, of what her GRE Q score might be.

1) Among the students in this trial who studied less than 25 hours, what is the highest GRE Quant score achieved?

3) Among the students in this trial who studied for 20 hours or more, what fraction of them performed worse than expected, according to the best-fit line model? Express your answer as a fraction.

Re: Fifteen college seniors, none of whom took any math classes [#permalink]
15 Oct 2017, 01:05

Q1: Among the points representing those students who study less than 25 hours, the highest is the second from the right whose score can be read on the y axis as 154 (C)

Q2: The three students with the highest GRE scores have studied roughly 28, 43 and 45 hours. Thus the mean is 28+43+45/3 = 38.6 which can be rounded to 39. (D)

Q3: To compute the ratio of those scoring less than expected, we can compute the denominator as the sum of the points after 20 hours of study and at the numerator those below the fit line. This leads to a ratio of 3/10