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!

Homework Help: Marginal Probability Function

  1. Nov 23, 2008 #1
    I have this question which I cannot seem to solve:
    The joint probability mass function p(x, y) of two discrete random variables X and Y is given by.
    p(x,y) = ([5^x][7^y][e^-5])/x!(y-x)!
    x and y are non-negative integers and x <= y
    (i) Find the marginal probability mass functions of X and Y.
     
  2. jcsd
  3. Nov 23, 2008 #2
    You would have to "integrate out" the dependence on the second variable. Explicitly

    [tex]
    p(x)=\sum_{y\geq x}p(x,y)
    [/tex]
    and
    [tex]
    p(y)=\sum_{x\leq y}p(x,y)
    [/tex]
    By the way, you joint pmf doesn't sum to one, but to e37.
     
  4. Nov 23, 2008 #3
    but how do i integrate the factorials?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook