The college bookstore tells prospective students that the average cost of its textbooks is $90 per book with a standard deviation of $15. The engineering science students think that the average cost of their books is higher than the average for all students. To test the bookstore’s claim against their alternative, the engineering students collect a random sample of size 45.
a. If they use a = 0.05 what is the critical value of the test statistic?
b. The engineering students’ sample data are summarized by n _ 45 and ∑x = 4380.30. Is this sufficient evidence to support their contention?