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Variables and their common density

  1. May 11, 2013 #1
    we have X,Y variables and their common density f(m,n)=P(X=m,Y=n) where f(0,1)=0.1 f(1,0)=0.1
    and f(1,1)=0,31 find P(X=0)

    i think that P(X=0)= f(0,1) but it says that its incorrect what i am doing wrong?
     
  2. jcsd
  3. May 11, 2013 #2

    mfb

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    I think you need more data.
    Do you know that X and Y are independent? (my guess)
    Do you know something else about X and Y?

    Why do you think that? Does Y have to be 1 if X is 0?
     
  4. May 11, 2013 #3
    the exercise gives only this data... its say that X,Y ,they take 0 and 1 each of them..
     
  5. May 11, 2013 #4

    Ray Vickson

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    You can determine f(0,0) by using the fact that the f(i,j) must sum to 1. What does the event {X=0} look like as a subset of the whole allowed (X,Y) space S= {(0,0),(0,1),(1,0),(1,1)}?
     
  6. May 11, 2013 #5
    i must estimate f(0,0)?
     
  7. May 11, 2013 #6

    Ray Vickson

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    What do YOU think?
     
  8. May 12, 2013 #7
    i dont understand how to solve this
     
  9. May 12, 2013 #8

    Ray Vickson

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    That must mean that you did not read my first response.
     
  10. May 12, 2013 #9
    i read it but i dont understand very well english....may can u explain it more specifical
     
  11. May 12, 2013 #10

    haruspex

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    There are four combinations possible: 00, 01, 10, 11. You know the probabilities of three of these. So what is the probability of the fourth?
     
  12. May 12, 2013 #11
    yea but what is the diference between 0.1 and 0,1 because he gives me decimal point and not 0,1
     
  13. May 12, 2013 #12

    mfb

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    0.1 is a number, (0,1) are two numbers, here used for X and Y.
     
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