Originally Posted by

**braddy**

*problem 2:*

**A traffic engineer is studying the number of vehicles that arrive, during a certain 2-minute period, at two streets corners that are close to each other. Let X be the number of vehicles at on street corner and Y the number at the other. The enginner knows the joint distribution probability distribution of X and Y is:**

**-f(x,y)=(9/16)*(1/4)^(x+y), x=0,1,2,3..., y=0,1,2,....**

**- 0 elsewhere**

**For example P(X=1,Y=1)=0.035.**

**The enginner calculated E(X)=E(Y)=1/3, and Var(X)=Var(Y)=4/9.**

**He has calculated that X and Y are independent.**