Wikipedia:Reference desk/Archives/Mathematics/2008 April 12

From Wikipedia, the free encyclopedia

Mathematics desk
< April 11 << Mar | April | May >> April 13 >
Welcome to the Wikipedia Mathematics Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.


Contents


[edit] April 12

[edit] Statistics

This is a homework question but I've done the first bit of legwork for myself and I'm only asking for a hint.

There is a biased six sided diced such that the probability of getting a six is three times the probability of getting a 1, 2, 3, 4 or 5. This means that p(1)=0.125 and p(6)=0.375. Having worked out the expected value of X as 4.125, how do I calculate the variance? Thanks 92.0.233.217 (talk) 14:55, 12 April 2008 (UTC)

For a random variable X with expected value m, the variance of X is the expected value of (X-m)2. You know that m is 33/8 or 4.125. So take each of the possible values of X, the number thrown on the dice; calculate (X-4.125)2; multiply this by the probability of throwing that number; and add these 6 values together. Gandalf61 (talk) 16:16, 12 April 2008 (UTC)