如题所述
(1)X1的期望为E(X1)=1*P(X1=1)+2*P(X1=2)+3*P(X1=3)=2
(2)Var(X3)=E【X3-E(X3)】^2=(1-2)^2*P(X3=1)+(2-2)^2*P(X3=2)+(3-2)^2*P(X3=3)=2/3追问
(2)Var(X3)=E【X3-E(X3)】^2=(1-2)^2*P(X3=1)+(2-2)^2*P(X3=2)+(3-2)^2*P(X3=3)=2/3追问
答案是4/3和73/9
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