The Comfy Company sells medium-priced patio furniture through a mail-order catalog. It has operated primarily in the East but is now expanding to the Southwest. To get off to a good start, it plans to send potential customers a catalog with a discount coupon, However, Comfy is not sure how large a discount is needed to entice customers to buy It experiments by sending catalogs to selected residents in six cities. Tucson and San Diego receive coupons for 5% off any furniture within the next months, Phoenix and Santa Fe receive coupons for 10% off, and Riverside and Albuquerque receive coupons for 15% off. Comfy wonders whether there are differences across pairs of cities that receive the same discount.

a. Find a 95% confidence interval for the difference between the mean amount spent in Tucson and the similar mean in San Diego. (These means should include the "O purchases.") Repeat this for the difference between Phoenix and Santa Fe and then between Riverside and Albuquerque. Does city appear to make a difference?

b. Repeat part a. but instead of analyzing differences between means, analyze differences between proportions of customers who purchase something. Does CIO' appear to make a difference?