Help with standard deviation & expected value please

• Jul 25th 2012, 10:06 PM
numbaoneazn1
Help with standard deviation & expected value please
x -5 -1 2 7 10
P(x)0.15 0.08 0.22 0.18 0.37

Determine the expected value of x.

Determine the standard deviation of x.
• Jul 26th 2012, 01:45 AM
$E(X)=\Sigma_{i=1}^{n}x_iP(x_i)}$
$SD(X)=\sqrt{\Sigma_{i=1}^{n}\left[x_i-E(X)\right]^2P(x_i)}}$ or
$SD(X)=\sqrt{E(X^2)-E(X)^2}$