Mean Questions

Let $x_1,x_2,\dots ,x_n$ be $n$ observations such that $\sum x_i^2=400$ and $\sum x_i=80$. Then a possible value of $n$ among the following is:

The mean of the numbers $a,b,8,5,10$ is $6$ and the variance is $6.80$. Then which one of the following gives possible values of $a$ and $b$?

Let $x_1,x_2,\dots ,x_n$ be $n$ observations, and let $\bar{x}$ be their arithmetic mean and ${\sigma }^2$ be their variance.Statement 1: Variance of $2x_1,2x_2,\dots ,2x_n$ is $4{\sigma }^2$.Statement 2: Arithmetic mean of $2x_1,2x_2,\dots ,2x_n$ is $4\bar{x}$.