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Solution

Numbers are $2,4,\dots,100=2\cdot{1,\dots,50}$. $\operatorname{Var}(1,\dots,50)=\dfrac{50^2-1}{12}=\dfrac{2499}{12}=\dfrac{833}{4}$. Scaling by $2$: $\operatorname{Var}=4\cdot\dfrac{833}{4}=833$.