What is the variance of 25 consecutive multiples of 3, such as 3, 6, 9, …, 75?

For $n$ consecutive integers the variance is $\frac{n^2-1}{12}=\frac{624}{12}=52$. Multiplying by 3 multiplies the variance by 9: $9\times 52=468$. (156 multiplies by 3 only.)