1.
A data consists of nn observations: x1,x2,,xnx_1, x_2, \ldots, x_n. If i=1n(xi+1)2=11n\sum_{i=1}^{n}(x_i+1)^2 = 11n and i=1n(xi1)2=7n\sum_{i=1}^{n}(x_i-1)^2 = 7n, then the variance of this data is