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Math Help - what is the difference?

  1. #1
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    what is the difference?

    Hi all,

    In this type normal distribution questions which include "sample", I don't know how to use this sample to solve the question. What is the difference between normal distribution problems and normal sampling questions? I really do have difficulty in solving these type of questions.




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  2. #2
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    Re: what is the difference?

    Surely somewhere in your text book is the fact that if a random variable has mean \mu and standard deviation \sigma then a sample of size n will be (approximately) normally distributed with mean n\mu and standard deviation \sigma\sqrt{n}.
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  3. #3
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    Re: what is the difference?

    For the 1st problem:

    z= x-μ (x sample)
    ---------------------
    σ/ n (square root)

    μ= 95.25
    σ= 27.32
    n= 25

    102.50 - 95.25
    -----------------------
    27.32 / 25 (square root)

    7.25
    ----- = 1.326 ~ 1.33 = 0.4082
    5.464

    1-0.4082 = 0.5918

    Is the answer correct?
    Last edited by Liliann; June 6th 2014 at 11:22 AM.
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  4. #4
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    Re: what is the difference?

    For the 2nd problem:

    230-237.6
    ---------------------
    26.3 / 55 (square root)

    -7.6
    = -------------- = -2.143 ~ 2.14
    26.3/7.417

    = 1-0.9838 = 0.0162
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  5. #5
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    Re: what is the difference?

    I do not know whether or not my answers are correct.
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  6. #6
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    Re: what is the difference?

    Quote Originally Posted by Liliann View Post
    For the 1st problem:

    z= x-μ (x sample)
    ---------------------
    σ/ n (square root)

    μ= 95.25
    σ= 27.32
    n= 25

    102.50 - 95.25
    -----------------------
    27.32 / 25 (square root)

    7.25
    ----- = 1.326 ~ 1.33 = 0.4082
    5.464

    1-0.4082 = 0.5918

    Is the answer correct?
    No.

    The probability associated with z-score 1.33 is about 0.907724, not 0.4082 as you have here. Did you forget the 1/2 you sometimes need to adjust your table value?
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  7. #7
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    Re: what is the difference?

    Quote Originally Posted by Liliann View Post
    For the 2nd problem:

    230-237.6
    ---------------------
    26.3 / 55 (square root)

    -7.6
    = -------------- = -2.143 ~ 2.14
    26.3/7.417

    = 1-0.9838 = 0.0162
    Nope. You dropped a negative sign.
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  8. #8
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    Re: what is the difference?

    Quote Originally Posted by romsek View Post
    Nope. You dropped a negative sign.
    Thanks you very much for your help, sir.

    I've corrected the mistakes.
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