Question 125696
You need to subtract the mean from EACH of the 30 data points.
Then square EACH of the differences.
Then add up all of the squared differences.
Divide this sum of squares by the number of data points minus 1 (29) (this is because you are doing a sample of a population).
Take the square root of the quotient.


{{{sigma=sqrt((1/(N-1))*sum((x[i]-x[bar])^2,i=1,N))}}}  {{{x[bar]}}} is the mean of your sample.


Drop me a line and I'll send you a spreadsheet that shows all of the calculations.