how do you find the standard deviation

For a list of data, you would:

1) Find the average (mean) of all the data numbers. (Add all of the numbers, then divide by how many numbers there are in the list).

2) Take each number in the original data list and subtract that average number from each data number. Then, square the result. You should now have a new list of numbers.

3) Find the average of all the numbers in this new list.

4) Take the square root of that average, which is the standard deviation for that data.

This page can explain the process more clearly: http://www.mathsisfun.com/data/standard-deviation-formulas.html

As a side note, you can also use a calculator such as a TI-84 to calculate standard deviation. On the TI-84, enter the data as a list in "2nd" "LIST".

Then go to "2nd" "LIST" => "MATH" => "7stdDEV( " and press "Enter".

Then go to "2nd" "LIST" and select the list number. Press "Enter" and the standard deviation will show up.

Thank you Kitty.  How pretty, and informative is that!