Student2013

The distribution of men's heights has a mean of 68in, standard deviation of 2.5in. If the heights of brothers have a correlation of 0.5, what is the mean and variance of the difference in heights between pairs of brothers? I know that r=Cov(x,y)/(sqrt(V(x)V(y)) so 0.5=Cov(x,y)/(sqrt(2.52)(V(y)) but then I'm stuck trying to solve the Cov since they arent independent, E(xy) does not equal E(x)E(y) I have the solution, can't see how to get there. The solution: mean=0, variance=6.25