If the variance of the first ‘n’ natural numbers is 10 and the variance of the first ‘m’ even natural numbers is 16, then m + n is equal to ____.

$Var\left(1,2,\mathrm{........},n\right)=10\Rightarrow \frac{1^2+2^2+\mathrm{.......}+n^2}{n}-{\left(\frac{1+2+\mathrm{......}+n}{n}\right)}^2=10$

$\Rightarrow \frac{\left(n+1\right)\left(2n+1\right)}{6}-{\left(\frac{n+1}{2}\right)}^2=10$

$\Rightarrow n^2-1=120\Rightarrow n=11$

$Var\left(2,4,6,\mathrm{.......},2m\right)=16\Rightarrow \mathrm{var}\left(1,2,\mathrm{.....},m\right)=4$

$\Rightarrow m^2-1=48\Rightarrow m=7\Rightarrow m+n=18$