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Two independent X, Y with Var(X) = 4, Var(Y) = 9. Var(X + Y) =
A13 (independence: variances add)
B6.5
C36
Dsqrt(13)
Answer & Solution
Correct answer: A. 13 (independence: variances add)
For independent X, Y: Var(X + Y) = Var(X) + Var(Y) = 4 + 9 = 13. (For dependent: Var(X+Y) = Var(X) + Var(Y) + 2Cov(X,Y).)
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