# Thread: random var X's probability distribution

1. ## random var X's probability distribution

2. Originally Posted by ndcruz
Find $\mu=E(X)$, $\sigma^2$ and then $\sigma$

Recall that:

$\mu=E(X)=\sum_{x} xP(x)$

$\sigma^2=E(X^2)-\left[E(X)\right]^2=\left[\sum_x xP(x) \right]-\mu^2$

$\sigma=\sqrt{E(X^2)-\left[E(X)\right]^2}=\sqrt{\left[\sum_x xP(x) \right]-\mu^2}$

Do you think that you can solve the problem now?

--Chris