# Covariance question

by ank0006
Tags: correlation, covariance, expected value, probability, statistics
 P: 1 1. The problem statement, all variables and given/known data Let the random variables X and Y have the joint p.m.f.: f(x,y) = (x+y)/32 x=1,2, y=1,2,3,4. find the means $$\mu$$x and $$\mu$$y, the variances $$\sigma$$2x and $$\sigma$$2y, and the correlation coefficient $$\rho$$. 2. Relevant equations $$\rho$$=(COV(X,Y))/$$\sigma$$x$$\sigma$$y 3. The attempt at a solution I was able to find both $$\mu$$'s: $$\mu$$x= (25/16) $$\mu$$y= (45/16) and both variances: $$\sigma$$x=(63/256) $$\sigma$$y=(295/256) But I cant seem to find how to get the covariance...I tried just using the 1 and 2 values for x and y, but it hasn't worked. I think I'm getting confused because there are more y values than x values. Any help would be much appreciated!
 HW Helper P: 3,309 do you knw the formula for covariance? you will need to calculate 2x4 terms, one for each x & y outcome

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