Variance: Take each number and subtract from it the average. Square this difference. Now take all the squares and add them together. Divide by the # of numbers minus 1.
Standard Deviation: Square root of variance.
Example:
1, 2, 5, 6, 11
Average = 5
1-5 = -4
(-4)^2 = 16
2-5 = -3
(-3)^2 = 9
5-5 = 0
0^2 = 0
6-5 = 1
1^2 = 1
11-5 = 6
6^2 = 36
16 + 9 + 0 + 1 + 36 = 62
We have 5 numbers so take 62 / (5-1) = 62/4 = 15.5 is your variance.
Standard Deviation is sqrt(15.5) ~ 3.937
