The total number of three  digit numbers , the sum of whose digits is even , is equal to 

Let the number be $n=x_1,x_2,x_3$
Since  $x_1+x_2+x_3$ is even. That means there are following cases:
(i)  $x_1,x_2,x_3$ all are even 
   $\to \mathrm{4.5.5}=100ways$
(ii)  $x_1$ even and  $x_2,x_3$ are odd
    $\to \mathrm{4.5.5.}=100ways$
(iii)  $x_1$ odd, $x_2$  even,  $x_3$ odd
       $\to \mathrm{5.5.5.}=125ways$
(iv)  $x_1$ odd,  $x_2$ odd,  $x_3$ even
        $\to \mathrm{5.5.5.}=125ways$