A regression equation to be used to predict a dependent variable with four independent variables is developed from a sample of size 10. The resulting equation is yn = 32.8 + 0.470x1 + 0.554x2 - 4.77x3 + 0.929x4 Two other equations are developed from the sample:
yn = 12.4 + 0.60x1 + 1.60x2 and yn = 49.7 - 5.38x3 + 1.35x4 The respective sum of squares errors for the three equations are 201.72, 1,343, and 494.6.

a. Use the summary information to determine if the independent variables x3 and x4 belong in the complete regression model. Use a significance level of 0.05.

b. Repeat part a for the independent variables x1 and x2. Use the p-value approach and a significance level of 0.05.