Var(X + Y) = Var(X) + Var(Y) + 2·Cov(X,Y). For independent variables: Var(X + Y) = Var(X) + Var(Y). This extends to sums of n independent variables: Var(ΣXᵢ) = ΣVar(Xᵢ).
Multiple Discrete Random Variables
View .mdVar(X + Y) = Var(X) + Var(Y) + 2·Cov(X,Y). For independent variables: Var(X + Y) = Var(X) + Var(Y). This extends to sums of n independent variables: Var(ΣXᵢ) = ΣVar(Xᵢ).