A 10-year study conducted by the American Heart Association provided data on how age, blood pressure, and smoking relate to the risk of strokes. Data from a portion of this study follow. Risk is interpreted as the probability (times 100) that a person will have a stroke over the next 10-year period. For the smoker variable, 1 indicates a smoker and 0 indicates a nonsmoker. a. Develop an estimated regression equation that can be used to predict the risk of stroke given the age and blood-pressure level.
b. Consider adding two independent variables to the model developed in part (a),one for the interaction between age and blood-pressure level and the other for whether the person is a smoker. Develop an estimated regression equation using these four independent variables.
c. At a .05 level of significance, test to see whether the addition of the interaction term and the smoker variable contribute significantly to the estimated regression equation developed in part (a).

Risk Age Blood Pressure Smoker
12 57 152 0
24 67 163 0
13 58 155 0
56 86 177 1
28 59 196 0
51 76 189 1
18 56 155 1
31 78 120 0
37 80 135 1
15 78 98 0
22 71 152 0
36 70 173 1
15 57 135 1
48 77 209 1
15 60 199 0
36 82 119 1
8 66 166 0
34 80 125 1
3 62 117 0
37 59 207 1