1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Expected Value, Expected Variance,covariance

  1. Oct 7, 2007 #1
    Can someone help me with this problem????

    The joint probability mass function of X and Y, p(i,j)=P{X=i,Y=j}, is given as follows
    p(-1,-2)=1/9, p(-1,-1)=1/18, p(-1,0)=1/12, p(-1,1)=0,
    p(0,-2)=1/12, p(0,-1)=1/9, p(0,0)=0, p(0,1)=1/8,
    p(1,-2)=0, p(1,-1)=1/8, p(1,0)=1/4, p(1,1)=1/18,

    a) Compute the E[X], Var(X), and Cov(X,Y)
    b) Calculate P{X,Y=k} for k=-2,-1,0,1,2
    c) Evaluate E[Y|X=k] for k=-1,0,1

    here is what I attempted to do:
    E[X]=E[X1] + E[X2]+.............E[Xn]=np
    Var(X)= E[X^2]-(E[X])^2

    E[X]=E[X|Y=-2]= 1/9(-1)+1/12(0)+0(1)=-1/9
    E[X|Y=1]=0(-1) + 1/8(0) +1/18(1)=1/18

    now the variance Var(X)

    E[Y]= [Y|X=-1]=1/9(-2)+1/18(-1)+1/12(0)+0(1)=-5/18
    E[Y]=-5/18 -11/72-5/72=-41/72


    Could you check part A ...........I really need help with part b and c
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted