Question: The Iams Company sells Eukanuba and Iams premium dog and cat foods (dry and canned) in 70 countries. Iams makes dry dog and cat food at plants in Lewisburg, Ohio; Aurora, Nebraska; Henderson, North Carolina; Leipsic, Ohio; and Coevorden, the Netherlands. Its Eukanuba brand dry dog foods come in five formulas. One of the ingredients is of particular importance: crude fat. To discover if there is a difference in the average percentage of crude fat among the five formulas and among the production sites, the sample data found in the file titled Eukanuba were obtained.

a. Determine if there is interaction between the Eukanuba formulas and the plant sites where they are produced. Use the p-value approach and a significance level of 0.025.

b. Given your findings in part a, determine if there is a difference in the average percentage of crude fat in the Eukanuba formulas. Use a test-statistic approach with a significance level of 0.025.

c. Repeat part b for the plant sites in which the formulas are produced.

d. One important finding will be whether the average percent of crude fat for the "Reduced Fat" formula is equal to the advertised 9%. Conduct a relevant hypothesis test to determine this using a significance level of 0.05.