A cereal company wants to see which of two promotional strategies, supplying coupons in a local newspaper or including coupons in the cereal package itself, is more effective. (In the latter case, there is a label on the package indicating the presence of the coupon inside.) The company randomly chooses 80 Kroger's stores around the country—all of approximately the same size and overall sales volume—and promotes its cereal one way at 40 of these sites, and the other way at the other 40 sites. (All are at different geographical locations, so local newspaper ads for one of the sites should not affect sales at any other site.) Unfortunately, as in many business experiments, there is a factor beyond the company's control, namely, whether its main competitor at any particular site happens to be running a promotion of its own. The file P09_70.xlsx has 80 observations on three variables: Sales: number of boxes sold during the first week of the company's promotion Promotion Type:1 if coupons are in local paper, 0 if coupons are inside box Competitor Promotion:1 if main competitor is running a promotion, 0 otherwise a. Based on all 80 observations, (1) Calculate the difference in sample mean sales (promotion type 0 minus promotion type 1) between stores running the two different promotional types. Round your answer to one decimal place, if necessary. Indicate which sample mean is larger. Ads in local paper (2) Calculate the standard error of this difference. Round your answer to two decimal places, if necessary. (3) Calculate the 90% confidence interval for the population mean difference. Round your answer to one decimal place, if necessary. If your answer is negative number, enter "minus" sign. Lower Limit Upper Limit