# Finding variance without knowing mean?

1. Sep 29, 2008

Hi,

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
$$\Sigma x^{2}$$ = 1320
$$\Sigma$$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$$u^{2}$$ + 5$$u^{2}$$$$/5$$

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. Sep 29, 2008