What is the formula for standard deviation?

[experimental]

What is the formula for standard deviation?

 

[symbolipoint]

Have you tried either (1) an elementary textbook on Statistics, or (2) WikiPedia? In fact, check into this: http://en.wikipedia.org/wiki/Standard_deviation

What seems unusual, is "standard" deviation exists and is distinct from "average absolute value of the deviations".

 

[HallsofIvy]

You might also want to decide whether you are interested in the standard deviation of a probality distribution or of a sample from a probability distribution. The formulas are slightly different.

 

[waxwork]

This is a pretty good webpage:

http://standard-deviation.appspot.com/"