In a regression analysis involving 30 observations, the following estimated regression equation was obtained.

= 17.6 + 3.8x₁ 2.3x₂ + 7.6x₃ + 2.7x₄

For this estimated regression equation, SST = 1,840 and SSR = 1,810.(a)At = 0.05, test the significance of the relationship among the variables.Suppose variables

x₁ and x₄

are dropped from the model and the following estimated regression equation is obtained.

= 11.1 3.6x₂ + 8.1x₃

For this model, SST = 1,840 and SSR = 1,745.(b)Compute

SSE(x₁, x₂, x₃, x₄).

(c)Compute

SSE(x₂, x₃).

(d)Use an F test and a 0.05 level of significance to determine whether

x₁ and x₄

contribute significantly to the model.