Let Xi and Yi be random variables with Var(Xi) = σx2 and Var(Yi) = σy2 for all i ∈ {1, . . . , n}. Assume that each pair (Xi, Yi) has correlation Corr(Xi, Yi) = ρ, but that (Xi,Yi) and (Xj,Yj) are independent for all i ̸= j. (a) What is Cov(Xi,Yi) in terms of σx, σy and ρ? (b) Show that Cov(Xi,Y ̄) = (ρσxσy)/n, where Y ̄ is the average of the Yi (c) Determine Cov(X ̄,Y ̄).

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A: Result  If X and Y are independent then  E(g(X)h(Y))=E(g(X))E(h(Y)) Cov(X,Y)=0

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Q: Find the value of Var(X − 2Y + 7).

A: It is given that Var(X)=6, Var(Y)=3  and ρ(X, Y)=-14.