Statistics Questions

If the mean deviation of numbers $1,1+d,1+2d,\dots ,1+100d$ from their mean is $255$, then $d$ is equal to:

1: The variance of first $n$ even natural numbers is $\frac{n^2-1}{4}$.
2: The sum of first $n$ natural numbers is $\frac{n(n+1)}{2}$ and the sum of squares of first $n$ natural numbers is $\frac{n(n+1)(2n+1)}{6}$.