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

= April 12 =

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)