Question: Regressions often include interaction terms obtained by multiplying two of the right-hand side variables together. Consider the following regression:

Y = 9 + X₁ + 3X₂ - 0.20X₁X₂.

(a) What is the point estimate when X₁= 5 and X₂ = 1?

(b) Plot Y against X1 when X₂=0. On the same graph, plot Y against X₁ when X₂ = 3. Describe how the effect of X₁ on Y depends on the level of X₂ in this model.