11. The annual return per dollar for two different investment instruments is the outcome of a bivariate random variable (Xl ,X2 ) with joint moment-generating function Mx(t) = exp(u't + .5t't), where t = [~~l u = [:~il and

= [.225 X 10-3 -.3 X 10-3 ]

-.3 X 10-3 .625 X 10-3 •