Results 1 to 4 of 4

Math Help - Standard Deviation help.

  1. #1
    Newbie
    Joined
    Nov 2007
    Posts
    12

    Standard Deviation help.

    Just trying to revise with past exam papers.

    -------
    A firm recorded the number of orders recieved per weekduring 2002 to give the following frequency distribution:




    i) Find the mean number of orders recieved for that time period.

    Answer = 8.66

    ii) Find the standard deviation of the number of orders recieved

    Stuck on this one

    can anyone help please, i have an exam in january and i really wanna understand this.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    GAMMA Mathematics
    colby2152's Avatar
    Joined
    Nov 2007
    From
    Alexandria, VA
    Posts
    1,172
    Awards
    1
    How did you get a mean when the data was given in ranges? To find standard deviation, you want to subtract the mean from each and every sample point. Square that result. Now add up all of your results and divide by N - the # of total results. That is your variance. The square root of variance is standard deviation.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Nov 2007
    Posts
    12
    ok i understand now, I have to find the mid class values of the data first and work out the mean from there.

    One thing i dont understand though is when we have a table like the one above, why do we have to work out fx and fx(squared) ? As when I go to do the standard deviation, this is not stated in the standard deviation equation.

    Anyone? x
    Follow Math Help Forum on Facebook and Google+

  4. #4
    GAMMA Mathematics
    colby2152's Avatar
    Joined
    Nov 2007
    From
    Alexandria, VA
    Posts
    1,172
    Awards
    1
    Quote Originally Posted by leaaa View Post
    ok i understand now, I have to find the mid class values of the data first and work out the mean from there.

    One thing i dont understand though is when we have a table like the one above, why do we have to work out fx and fx(squared) ? As when I go to do the standard deviation, this is not stated in the standard deviation equation.

    Anyone? x
    That is the definition of standard deviation. That takes into account all values will then be positive. The sum of these squares is the variance, but to get back to our average difference from the mean, or standard deviation, you need to take the square root of that sum.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Standard Deviation
    Posted in the Statistics Forum
    Replies: 4
    Last Post: September 8th 2010, 04:05 AM
  2. Replies: 5
    Last Post: May 18th 2009, 05:14 AM
  3. standard deviation and mean deviation
    Posted in the Statistics Forum
    Replies: 1
    Last Post: March 16th 2008, 06:09 AM
  4. i need standard deviation help
    Posted in the Statistics Forum
    Replies: 2
    Last Post: February 22nd 2008, 06:03 PM
  5. The mean and standard deviation
    Posted in the Advanced Statistics Forum
    Replies: 3
    Last Post: February 17th 2008, 09:15 PM

Search Tags


/mathhelpforum @mathhelpforum