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Probability Random variables help

  1. May 17, 2009 #1
    1. The problem statement, all variables and given/known data

    Can anyone help me with question 5d on this paper, I just dont get it.

    I have done 5a,5b and 5c.

    How do I find the values for x1 and x2 ?

    http://www.mathspapers.co.uk/Papers/edex/S1Jan03Q.pdf [Broken]

    Thanks.
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. May 17, 2009 #2
    Let Y= X1 + X2

    then we want the probability that Y=5

    P(Y=5) = P(X1=2 , X2=3) + P(X1=3 , X2=3)

    and since X1 and X2 are independent

    P(Y=5) = P(X1=2)*P(X2=3) + P(X1=3)*P(X2=2)

    and then just find the probabilites from the given probability distribution function
     
    Last edited: May 17, 2009
  4. May 17, 2009 #3
    Oh I see that makes so much sense now, Thanks.
     
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