Refer to Examples 12.1 and 12.2. The collector of antique grandfather clocks knows that the price (y) received for the clocks increases linearly with the age 1x12 of the clocks. Moreover, the collector hypothesizes that the auction price (y) of the clocks will increase linearly as the number of bidders 1x22 increases. Use the information on the MINITAB printout shown in Figure 12.2 (p. 687) to

a. Test the hypothesis that the mean auction price of a clock increases as the number of bidders increases when age is held constant (i.e., when b2 7 0). (Use a = .05.)

b. Find a 90% confidence interval for b1 and interpret the result.