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

• November 19th 2009, 06:13 AM
Ttops
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.
• November 19th 2009, 09:04 PM
qmech
calculating mean and std dev
The mean (mu) is calculated by:
$
\mu = 1 * p(1) + 2 * p(2) + 3 * p(3) + ....
$

The standard deviation obeys a rule saying
$
\sigma ^ 2 = E(X^2) - (E(X)) ^ 2
$