Standard Deviation

[Amartya Sanyal]

There are multiple formulas for standard deviation and each of them apparently gives different values. Is there any fixed one to be used or does this stdev = sqrt((1/N)*((sum of squares) - (((sum)^2)/N))) suffice?

[Piyush P Kurur]

The two standard deviation formulas that you are talking about is actually two different statistical quantities namely.

1. Population standard deviation
2. Sample standard deviation.

In case 1 you need to divide by N which is the population size where as in case 2 you need to divide by (N-1) when N is the sample size.

For the problem, we are asking for the population sd not the sample sd.

[Piyush P Kurur]

I guess the question is now clarified