Variance of Summations Let X1,X2,...,Xn be random variables with finite variance,then we have var(∑iXi)=∑ivar(Xi)+∑jCoV(Xi,X) 6Variance of Summations • Let 𝑋1 , 𝑋2 , ⋯ ,𝑋𝑛 be random variables with finite variance, then we have var σ𝑖 𝑋𝑖 = σ𝑖 var(𝑋𝑖 ) + σ𝑖≠𝑗 cov(𝑋𝑖 ,𝑋𝑗 ) 6