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Binomial Distribution Help

  1. Nov 9, 2012 #1
    IF Y~B(11, 0.3), find (|Y-5| >= 3)

    I got the answer(0.3170) but i don't understand the logic behind this part where i am confused.

    can someone explain the working(second working) where i somehow got it blindly correct?


    ==================================
    my working at first:

    |Y-5| >= 3
    Y >= 8
    Y <=2

    so P( 2 >= Y >= 8)

    P(Y=8) = 0.9994
    1 - 0.9994 = 0.0006

    P(Y=2) = 0.3127

    so P( 2 >= Y >= 8) = 0.3133

    However this answer is wrong
    =================================

    =================================
    My second working:

    my working at first:

    |Y-5| >= 3
    Y >= 8
    Y <=2

    so P( 2 >= Y >= 8)

    P(Y=7) = 0.9957
    1 - 0.9957 = 0.0043

    P(Y=2) = 0.3127

    so P( 2 >= Y >= 8) = 0.3170

    This is the correct working but i don't understand why Y is = 7....
    =================================
     
  2. jcsd
  3. Nov 9, 2012 #2

    haruspex

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    Much clearer to write P( 2 >= Y | Y >= 8)
    That's the probability that Y <= 8. If you subtract that from 1 you'll have the probability that Y > 8.
     
  4. Nov 10, 2012 #3
    Thank you for your help. I'm getting the idea of it now.

    Cheers
     
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