13.23 Exercise 13.16 described a regression analysis in which y 5 sales revenue and x 5 advertising expenditure.

Summary quantities given there yield n 5 15 b 5 52.27 sb 5 8.05

a. Test the hypothesis H0: b 5 0 versus Ha: b Þ 0 using a significance level of .05. What does your conclusion say about the nature of the relationship between x and y?

b. Consider the hypothesis H0: b 5 40 versus Ha:
b . 40. The null hypothesis states that the average change in sales revenue associated with a 1-unit increase in advertising expenditure is (at most)
$40,000. Carry out a test using significance level .01.