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Math Help - Probability homework help again...

  1. #1
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    Probability homework help again...

    I'm very stuck here as I do not know how to add independant events! Here is the question:

    P(A) = 13/25
    P(B) = 9/25
    P(A|B)= 5/9

    Determine the probabilties...

    a) P(A or B or Both)
    b) P(A'|B')
    c) P(A occurs or B does not occur)

    What is the best way of tackling these problems?

    Thanks guys!
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  2. #2
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    Hello, anthmoo!

    Given: .P(A) = 13/25, .P(B) = 9/25, .P(A|B)= 5/9

    Determine the probabilties:.

    a) P(A U B) . . b) P(A'|B') . . c) P(A U B')

    I would use Bayes' Theorem, then draw a Venn diagram.

    . . . . . . . . . . . . . . . P(A ∩ B)
    We have: .P(A|B) .= .---------- .= .5/9
    . . . . . . . . . . . . . . . . . P(B)

    . . . . . . . . . . . . . . . . . . . . .P( A ∩ B)
    Since P(B) = 9/25, we have: .----------- .= .5/9
    . . . . . . . . . . . . . . . . . . . . . .9/25

    . . Hence: .P(A ∩ B) .= .1/5


    Now we can draw the Venn diagram.

    Code:
          *---------------------------------------------------*
          |                                                   |
          |                   *-----------------------*       |
          |                   |                     A |       |
          |                   |           8/25        |       |
          |                   |                       |       |
          |       *-----------+-----------*           |       |
          |       |           |           |           |       |
          |       |           |    1/5    |           |       |
          |       |           |           |           |       |
          |       |           *-----------*-----------*       |
          |       |                       |                   |
          |       |      4/25             |                   |
          |       | B                     |                   |
          |       *-----------------------*         8/25      |
          |                                                   |
          *---------------------------------------------------*
    You should be able to answer the questions now.

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  3. #3
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    Quote Originally Posted by Soroban View Post
    Hello, anthmoo!


    I would use Bayes' Theorem, then draw a Venn diagram.


    We haven't covered either of those =/ or anything with ∩ in..

    Is there any other way to do it?

    Is ∩ the same as | ? P(A|B) being the probability of A given that B has already occured.
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