I also see on the section on the Central Limit Theorem that the normal distribution is used and gives the graph of the 68/95/99 [rule](http://en.wikipedia.org/wiki/68%E2%80%9395%E2%80%9399.7_rule). However, I haven't seen the actual math used to prove this or how it gets computed. Can anyone give me a link or explain/show how the math behind the statement is done?