The owner of a chain of ice cream stores would like to study the effect of atmospheric temperature on sales during the summer season. A sample of 21 consecutive days is selected, with the following results (Hint: Determine which are the independent and dependent variables)
Temperature Sales
63 1.52
70 1.68
73 1.8
75 2.05
80 2.36
82 2.25
85 2.68
88 2.9
90 3.14
91 3.06
92 3.24
75 1.92
98 3.4
100 3.28
92 3.17
87 2.83
84 2.58
88 2.86
80 2.26
82 2.14
76 1.98
a. Assuming a linear relationship, use the least-square method to find the regression coefficients b0 and b1.
b. Predict the sales per store for a day in which the temperature is F.
c. Plot the residuals versus the independent variable by using Excel. (Shown in the Excel file)
d. Draw the normal probability plot by using Excel. (Shown in the Excel file)
e. Based on the results of (c) and (d), is there reason to question the validity of the model?