For 10 observations x1,x2,…,x10x_{1}, x_{2}, \dots, x_{10}x1,x2,…,x10, if ∑i=110(xi+2)2=180\sum\limits_{i=1}^{10} (x_{i}+2)^{2}=180i=1∑10(xi+2)2=180 and ∑i=110(xi−1)2=90\sum\limits_{i=1}^{10} (x_{i}-1)^{2}=90i=1∑10(xi−1)2=90, then their standard deviation is :
2
3\sqrt{3}3
222 \sqrt{2}22
3