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Homework Help: Mutually exclusive stats homework

  1. Feb 27, 2007 #1
    1. The problem statement, all variables and given/known data
    Suppose that P(A) = 0.8 and P(A or B) = 0.9 , determine P(B) If
    a) A and B are independent
    b) A and B are mutually exclusive


    2. Relevant equations
    for Independence P(A and B) = P(A) x P(B)
    for Mutually Exclusive P(A or B) = P(A) + P(B)


    3. The attempt at a solution
    for A) just by the formula i can say that P(A and B) = P(A) x P(B)
    but i dont see still how i can find P(B), the P(A or B) part is really confusing to me.
     
  2. jcsd
  3. Feb 28, 2007 #2

    HallsofIvy

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    For not mutually exclusive, part (A), p(A or B)= P(A)+ P(B)- P(A and B). Put the values into both that AND P(A and B)= P(A)xP(B).
     
  4. Feb 28, 2007 #3
    hm thanks, but how do you find out what P(B) alone is cuz i cant use that formula anyways.
     
  5. Feb 28, 2007 #4

    HallsofIvy

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    You can't use WHAT formula? And why not?
     
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