Statistics

A data consists of 20 observations $x_1, x_2, \ldots, x_{20}$. If $\sum\limits_{i=1}^{20}\left(x_i+5\right)^2=2500$ and $\sum\limits_{i=1}^{20}\left(x_i-5\right)^2=100$, then the ratio of mean to standard deviation of this data is :