Combining random variables: If X and Y are independent: E(X + Y) = E(X) + E(Y) and Var(X + Y) = Var(X) + Var(Y).
How to apply it: Variances add for independent random variables regardless of whether you add or subtract the variables; standard deviations do not add.
Course: AP Statistics · Unit: Probability, Random Variables, and Probability Distributions
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