# K-Sided Dice

• November 22nd 2008, 02:38 AM
waxandshine
K-Sided Dice
Hi everyone,

Looking for a bit of help. If i throw a k-sided dice twice, what is the expected value of their sums. I'm looking for a formula for it including k.

Thanks
• November 22nd 2008, 03:08 AM
CaptainBlack
Quote:

Originally Posted by waxandshine
Hi everyone,

Looking for a bit of help. If i throw a k-sided dice twice, what is the expected value of their sums. I'm looking for a formula for it including k.

Thanks

The expected value of the sum of two RV's is the sum of their expected values.

So what is the expected value of a single throw of a k-sided die.

CB
• November 22nd 2008, 09:26 AM
waxandshine
well yeah, but there's no values so it's basically the expected value of one roll times two, but i dont know hot to write a formula for the expected value of one roll
• November 22nd 2008, 10:27 AM
CaptainBlack
Quote:

Originally Posted by waxandshine
well yeah, but there's no values so it's basically the expected value of one roll times two, but i dont know hot to write a formula for the expected value of one roll

Fair die so probability of each face is 1/k.

So expected value is:

$
(1)(1/k)+(2)(1/k)+..+(k)(1/k)=(1/k)\sum_{i=1}^k i
$

CB