Results 1 to 2 of 2

Thread: Standard deviation

  1. #1
    Super Member
    Joined
    Mar 2014
    From
    malaysia
    Posts
    902
    Thanks
    2

    Standard deviation

    I know that the standard deviation of sample = standrad deviation of population divided by sqrt(n) ...

    However , in the following question , i dont know how to identify whether the standard deviation given is standard deviation of sample or standard deviation of population ...... Can anyone help me to idenitify it ?

    At a large university , the mean age of students is 22.3 years and the standard deviation is 4 years . A random sample of 64 students is drawn . What is the probability that the average of these students is greater than 23 years ?

    Based on the author , the 4 given is standard deviation of population .
    Th standard deviation of mean is 4 / sqrt(64) ..

    Why is it so ?
    I think it's wrong because we only picked 64 students out of the population , so the standard deviation we get is the standard deviation of sample , not the standard deviation of population
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Apr 2005
    Posts
    19,462
    Thanks
    2893

    Re: Standard deviation

    You are told that "the standard deviation is 4 years" before a sample is mentioned so that can't be the standard deviation of the sample! The standard deviation of the sample of 64 students is \frac{4}{\sqrt{64}}= \frac{4}{8}= \frac{1}{2}.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 2
    Last Post: Jun 5th 2014, 06:34 PM
  2. standard deviation
    Posted in the Statistics Forum
    Replies: 0
    Last Post: Mar 11th 2013, 03:00 AM
  3. Replies: 5
    Last Post: May 18th 2009, 05:14 AM
  4. standard deviation and mean deviation
    Posted in the Statistics Forum
    Replies: 1
    Last Post: Mar 16th 2008, 06:09 AM
  5. i need standard deviation help
    Posted in the Statistics Forum
    Replies: 2
    Last Post: Feb 22nd 2008, 06:03 PM

/mathhelpforum @mathhelpforum