# Expect value and standard deviation

• Feb 17th 2013, 07:14 PM
kkar
Expect value and standard deviation
Is there a way to calculate these two quantities if I'm throwing two twelve sided die and adding the results that's easier than going through all possible combination and their probabilities?

Thanks.
• Feb 17th 2013, 07:35 PM
Plato
Re: Expect value and standard deviation
Quote:

Originally Posted by kkar
Is there a way to calculate these two quantities if I'm throwing two twelve sided die and adding the results that's easier than going through all possible combination and their probabilities?

Look at this webpage

Scroll down to the fully expanded form of the expression.
That gives you all the impossibles.

For example the term $11x^{14}$ tells us that there eleven ways to roll a sum of fourteen. So the probability is $\frac{11}{144}$ of getting a sum of fourteen.
• Feb 18th 2013, 11:25 AM
kkar
Re: Expect value and standard deviation
Thanks Plato!