QSR reports on the largest quick-serve and fast-casual brands in the United States. The file FastFoodChain contains the food segment (burger, chicken, pizza, or sandwich) and U.S. mean sales per unit ($ thousands) for each of 38 quick-service brands. (Data extracted from bit.ly/16GJlEn.)

a. At the 0.05 level of significance, is there evidence of a difference in the mean U.S. mean sales per unit ($ thousands) among the food segments?

b. At the 0.05 level of significance, is there a difference in the variation in U.S. average sales per unit ($ thousands) among the food segments?

c. What effect does your result in (b) have on the validity of the results in (a)?