13.15 Exercise 13.10 summarized data on y 5 hardness of molded plastic and x 5 time elapsed since the molding was completed.

Summary quantities included n 5 15 b 5 2.50 SSResid 5 1235.470 o

sx 2 xd2 5 4024.20

a. Calculate the estimated standard deviation of the statistic b.

b. Obtain a 95% confidence interval for

b, the slope of the population regression line. (Hint: See Example 13.4.)

c. Does the interval in Part

(b) suggest that b has been precisely estimated? Explain.