1.
If ∑i=110(xi−15)=12\displaystyle\sum_{i=1}^{10}(x_i - 15) = 12 and ∑i=110(xi−15)2=18\displaystyle\sum_{i=1}^{10}(x_i - 15)^2 = 18, then the S.D. of observations x1,x2,…,x10x_1, x_2, \ldots, x_{10} is: