AP Statistics / Unit 2: Probability, Random Variables, and Probability Distributions

2.9 Parameters of Random Variables

3 practice questions

Notes

Mean (expected value): $\displaystyle \mu_X=\sum x_iP(x_i)$.
Standard deviation: $\displaystyle \sigma_X=\sqrt{\sum(x_i-\mu)^2P(x_i)}$.
Linear changes: $\mu_{a+bX}=a+b\mu_X$, $\sigma_{a+bX}=|b|\sigma_X$.
Sums of independent variables: means add; variances add.

Practice

$X$: values 0, 10 with probabilities 0.6, 0.4. $E(X)=$

$\sigma_X=3$. $\sigma_{2X+5}=$

For independent $X$ and $Y$, which add?

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