Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?