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Finding variance without knowing mean?

  1. Sep 29, 2008 #1

    my girlfriend is taking a business statistics class and she had a test today. she got stumped on a question and wrote it down so she could ask me about it when she got back since I'm pretty good at math. I tried solving it but from what i can tell it seems like you would need to know the mean in order to find the variance. the question is below:

    Find the Variance:

    n = 5
    [tex]\Sigma x^{2}[/tex] = 1320
    [tex]\Sigma[/tex]x = 80

    I expanded out the variance formula. since we run from i=1 to n (where n=5)
    I got the formula V = 1320 - 160[tex]u^{2}[/tex] + 5[tex]u^{2}[/tex][tex]/5[/tex]

    where u = the mean.

    My girlfriend says that the mean was not specified in the problem. I would have given my answer for the variance as a function of the mean as you can see above, but since this is a business statistics class i have the tendency to believe the teacher is expecting a numerical answer. Does anyone have any insight into how this problem can be solved, or is there not enough information given?

    Thank you.
  2. jcsd
  3. Sep 29, 2008 #2
    note: in the variance formula that i expanded out, i meant for the entire numerator to be divided by 5. (n=5)
  4. Sep 29, 2008 #3
    crap i just realized that i wasn't supposed to post this under here. i would delete it but i haven't figured out how yet. until i do i apologize.
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