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Math Help - finding a proportion ........

  1. #1
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    finding a proportion ........

    I would like to get some help in finding a proportion considering that :
    mean = 70 inches
    standard deviation = 2.8 inches

    What proportion of men are less than 68 inches tall? By the way , does someone can tell me what to do in order to do this problem with a ti-84/83 using the function called normalcdf ? Because I don't want to use the standard normal table . Thanks in advance.
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  2. #2
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    Quote Originally Posted by skorpiox View Post
    I would like to get some help in finding a proportion considering that :
    mean = 70 inches
    standard deviation = 2.8 inches

    What proportion of men are less than 68 inches tall? By the way , does someone can tell me what to do in order to do this problem with a ti-84/83 using the function called normalcdf ? Because I don't want to use the standard normal table . Thanks in advance.
    Calculate Pr(X < 68).

    Your calculator manual (also available on-line from the TI homepage, follow the links) will outline how to use your calculator. You will need to use -1E99 as good approximation to -oo in this context.
    Last edited by mr fantastic; June 30th 2009 at 03:08 AM. Reason: Fixed a typo
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  3. #3
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    The answer is .2389 ; however , whenever I try on my calculator , I obtain .23753. The procedure I use is normalcdf(-1 e 99, 68, 70 , 2.8) , and I'm not sure whether that's ok or not. Anyway , thanks for your time Mr. Fantastic.
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  4. #4
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    Quote Originally Posted by skorpiox View Post
    The answer is .2389 ; however , whenever I try on my calculator , I obtain .23753. The procedure I use is normalcdf(-1 e 99, 68, 70 , 2.8) , and I'm not sure whether that's ok or not. Anyway , thanks for your time Mr. Fantastic.
    0.23753 is correct (to five decimal places).

    0.2389 has probably been got using tables (which are not as accurate as technology).
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