The accompanying data on x = average energy density (calories per 100 grams) and y = average cost (in dollars) for eight different food groups are from the paper €œThe Cost of U. S. Foods as Related to Their Nutritional Value€(American Journal of Clinical Nutrition [ 2010]: 1181€“ 1188).
The authors were interested in the relationship between average cost and the average energy density of foods.

a. Construct a scatterplot of these data. Does the relationship between cost and energy density look approximately linear?
b. Find the equation of the least squares regression line.
c. Construct a residual plot and comment on any unusual features of the residual plot.
d. Compute and interpret the value of r2 in the context of this study.
e. Explain why it would also be informative to look at the value of s e in addition to the value of r2 in evaluating the usefulness of the least squares regression line.
f. Compute and interpret the value of s e .
g. Based on you answers to Parts (c) €“ (f), do you think it is appropriate to use the least squares regression line to predict average cost for a food group based on its average energy density? Explain.
h. The meat, poultry, and fish food group has an average energy density of 196. What average cost would you predict for this food group?

Average Average Energy Food Group Milk and milk products Eggs Dry beans, legumes, nuts Cost 0.40 0.32 0.50 Density 182 330 337 and seeds Grain products Fruit Vegetables Fats, oils, and salad dressings 0.37 Sugars, sweets and beverages 040 0.47 0.28 0.33 83 390 242