A statistics professor was handing out midterm grade slips on a Friday which happened to be the day before the school€™s Spring break. He noticed that there were an unusually large number of students missing from class that day. So he collected the leftover grade slips and created the data in Table 6.24 that summarized the midterm grades (out of a possible 100) for students that attended and missed class.

Table 6.24

(a) The professor had reason to suspect, before even looking at the data, that, in general, students who missed class would tend to have lower mean midterm grades. Write down the null and alternative hypotheses that he should use to test this suspicion using this class as a sample.
(b) Carry out the test in part (a). You may assume that the data for both groups are reasonably symmetric and have no strong outliers.
(c) Can we conclude on the basis of this test that skipping class on the day before break tends to hurt students€™ grades?
(d) There was one student who had stopped coming to class after the first week and thus had mostly zero grades and an extremely low midterm average. The instructor did not include that student when computing the statistics for Table 6.24. Was that a good decision? Explain.

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Std. Dev. Mean п In class Missed class 15 80.9 11.07 68.2 9.26