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Can someone please explain how to compute the mean and standard deviation for this qu

I wasnt sure where to post this question but since it`s stats, i decided to post it here.

p(x)=(1/4)(3/4)^(x-1), X=1,2,3,4

I'm totally confused on how to do it...the question and answer is in the word.doc provided but i need an explanation on how the answer is created.

Thank you.

calculating mean and std dev

The mean (mu) is calculated by:

$\displaystyle

\mu = 1 * p(1) + 2 * p(2) + 3 * p(3) + ....

$

The standard deviation obeys a rule saying

$\displaystyle

\sigma ^ 2 = E(X^2) - (E(X)) ^ 2

$