Ask Me Help Desk - Please help I swear I am statistically challenged.

If the 10 data points were randomly selected from a larger group of data, then you use N-1 in the denominator. This calculation gives a "sample standard deviation." The formula for sample standard deviation is:

$ s = \sqrt { \frac 1 {N-1} \displaystyle \sum_ {i=1} ^N (x_i - \bar x ) ^2 } $

But if in fact there are only 10 data points in total for the complete population, then you determine the standard deviation of the full population using N in the denominator, not N-1:

$ \sigma = \sqrt { \frac 1 N \displaystyle \sum_ {i=1} ^N (x_i - \mu ) ^2 } $

For this problem you should be using this second formula, since there were exactly 10 students. So you have:

$ \sigma = \sqrt { \frac 1 {10} \left( (2-5.6)^2 + (4-5.6)^2 + (22-5.6)^2 + ... + (4-5.6)^2 \right ) } $