Solve the equation
Question:

If $\sum_{\mathrm{i}=1}^{9}\left(\mathrm{x}_{\mathrm{i}}-5\right)=9$ and $\sum_{\mathrm{i}=1}^{9}\left(\mathrm{x}_{\mathrm{i}}-5\right)^{2}=45$, then the standard deviation of the 9 items $\mathrm{x}_{1}, \mathrm{x}_{2}, \ldots . . \mathrm{x}_{9}$ is

1. 4

2. 2

3. 3

4. 9

Correct Option: , 2

Solution: