96 Refer to Exercise 95.

a. Using no information about x , estimate and calculate a 95% confidence interval for the mean value of y . [ Hint: Use one-sample t methodology .]

b. Plot the estimated mean value and the confidence interval as horizontal lines on your scatterplot.

c. Compare the confidence intervals you calculated in parts c and d of Exercise 95 with the one you calculated in part a of this exercise. Does x appear to contribute information about the mean value of y ?

d. Check the answer you gave in part c with a statistical test of the null hypothesis H0: b1 = 0 against Ha: b1  0. Use a = .05.