Questions 20 and 21 refer to the following setup Suppose tha

Questions 20 and 21 refer to the following setup: Suppose that X and Y have the following joint probability distribution: 20. What is the P(X+Y=5)? Answer: 21. What is the COV(X,Y)?

Solution

20. P(X+Y=5)=(P(Y=1),P(X=4))+P(Y=3),P(X=2)=0.15+0.20=0.35

21.Cov(XY)=E(XY)-E(X)E(Y)

=(1*2*0.10+…+5*4*0.15)-(1*0.10+1*0.15+…+5*0.15)(2*0.10+…+4*0.15)

=9.6-3*3.2=0