Central Limit Theorem
From Qwiki
Let
be independent, identically distributed random variables with zero mean and finite variance. Let 
the random variable
has a Gaussian distribution
![P(y) = \frac{1}{\sqrt{2\pi\sigma^2}}\exp\left[-\frac{y^2}{2 \sigma^2}\right]](/images/math/3/0/d/30d5fea39488630c6862a571d527c1d7.png)
The proof of this theorem is an exercise in Transformation of Random Variables.
Explanation from MathWorld: http://mathworld.wolfram.com/CentralLimitTheorem.html

