# standard deviation help please!!

• Apr 16th 2009, 07:07 PM
SR rzperez27
standard deviation help please!!
A small-business owner must hire seasonal workers as the need arises. The following list shows the number of employees hired monthly for a 5-month period.

4, 13, 5, 6, 9

If the mean of these data is approximately 7, what is the population standard deviation for these data?

I have never done standard deviation in my class before-this question was from a sample of the CAHSEE. Please help and explain how I can do this problem.
• Apr 17th 2009, 12:37 AM
Twig
hi
hi

Do you know who to calculate the variance from sample?
You take every value and subtract from it the mean, then you square this number, and do this for all data.
that is,

$\mbox{Variance } = s^{2} = \frac{1}{n-1} \sum_{i=1}^{n} \, (x_{i} - \mu^{*})^{2}$

The standard deviation is the square root of the variance, so:

$\mbox {Standard deviation } = s = \sqrt{\frac{1}{n-1} \sum_{i=1}^{n} \, (x_{i} - \mu^{*})^{2}}$

The reason for dividing with (n-1) has to do with sample size, since n is small here, use (n-1), as written.