If the number of seven-digit numbers, such that the sum of their digits is even, is $m \cdot n \cdot…
If the number of seven-digit numbers, such that the sum of their digits is even, is $m \cdot n \cdot 10^{\mathrm{n}}$; $m, n \in\{1,2,3, \ldots, 9\}$, then $m+n$ is equal to _______
Solution
Total 7 digit nos. $=9000000$ 7 digit nos. having sum of digits Even $=4500000$ $=9.5 \cdot 10^5$ $\mathrm{m}=9, \mathrm{n}=5$ $\mathrm{m}+\mathrm{n}=14$