Steps:
1. Find out the actual mean of given data (X)
2. Find out the deviation of each value from the mean (x = X – X)
3. Square the deviations and take the total of squared deviations Σx2
4. Divided the total Σx by the number of observation (Σx2/n)
5. The square root of (Σx2/n) is standard deviation.
Σx2/n = Variance = Σ(x−x¯)2/n
When the sample size is less than 30, variance = Σ(x−x¯)2/n-1
When n = number of observations.