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Math Help - I can't figure this out...

  1. #1
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    I can't figure this out...

    Assume the random variable X is normally distrubted with mean = 50 and standard deviation = 7. Compute its probability.

    P(34 < X < 61)?
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by greenpumpkins View Post
    Assume the random variable X is normally distrubted with mean = 50 and standard deviation = 7. Compute its probability.

    P(34 < X < 61)?
    Compute the z-scores for the endpoints of the interval for X, then:

     <br />
P(34< X< 61)=P(-16/7<Z<11/7)=P(Z<11/7)-P(Z<-16/7) =\Phi(11/7)-\Phi(-16/7)<br />

    where \Phi(z) denotes the cumulative standard normal distribution, which you look up in a table.
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  3. #3
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    P(34 < X < 61) =

    P( X = 61) - P( X = 34)

    Using the formula Z = (X - Mean)/Std Deviation

    (61 - 50)/ 7 = 1.57

    (34 - 50)/7 = -2.28

    ɸ(1.57) - ɸ(-2.28)




    ɸ(-2.28) = 1-ɸ(2.28)

    As CB mentioned ɸ basically means look it up from a standard normal distribution table

    Hope this helps
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