Exercises $20.46-20.58$ require the use of a computer and software. Use a $5 \%$ significance level unless specified otherwise.
20.54 XR20-54 High levels of cholesterol can lead to heart attacks. For those with very high levels (above $7.5 \mathrm{mmol} / \mathrm{L}$ ), doctors prescribe drugs to reduce cholesterol levels. A pharmaceutical company has recently developed four such drugs. An experiment was conducted to determine whether any differences exist in their benefits. The company selected 25 groups of four men, each of whom
Because there are no national or regional standards, it is difficult for university admission committees to compare graduates of different high schools. University administrators have noted that an $80 \%$ average at a high school with low standards may be equivalent to a $70 \%$ average at another school with higher standards of grading. In an effort to more equitably compare applications, a pilot study was initiated. Random samples were drawn of students who had been admitted the previous year from four local high schools. All the students entered the business program with averages between $70 \%$ and $80 \%$. Their average grades in the first year at the university were computed. Can the university admissions officer conclude that there are differences in grading standards between the four high schools? (This exercise is identical to Exercise 15.14 except for the data.)