The mean of 100 observations is 50 and their standard deviation is 5 , then the sum of all squares of all the observations is

If both mean and variance of 50 observations $$x_1, x_2, \ldots, x_{50}$$ are equal to 16 and 256 respectively, then mean of $$\left(x_1-5\right)^2,\left(x_2-5\right)^2, \ldots \ldots,\left(x_{50}-5\right)^2$$ is

The variance of 20 observations is 5. If each observation is multiplied by 2, then variance of resulting observations is

Variance of first $$2 n$$ natural numbers is