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Probability formula

  1. Sep 29, 2009 #1
    1. Given P(AnB)=0.6 and P(A|B)=0.10, find P(B)



    2. P(A|B)=P(AnB)/P(B)




    3. I plugged in the numbers in the formula but keep getting that P(B) is 6.... which is wrong since P cannot be greater than 0. Am I doing something wrong?
     
  2. jcsd
  3. Sep 29, 2009 #2

    Mark44

    Staff: Mentor

    Instead of plugging in numbers, solve this equation algebraically for P(B):
    P(A|B)=P(AnB)/P(B)

    When you have P(B) isolated, substitute the values you have for the two other quantities.
     
  4. Sep 29, 2009 #3
    That's what I did.

    P(B)=P(AnB)/P(A|B)=0.6/0.1=6........but this makes no sense to me.
     
  5. Sep 29, 2009 #4

    Mark44

    Staff: Mentor

    I don't see anything wrong in your work, although obviously a probability can't be larger than 1. Are you sure you have the problem written the same as it was given to you?
     
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