How many 5 digit numbers are there such that sum of their digits is even.
First I thought when is the sum of 5 Digits is even. Well there are a lot of possible ways. But obviously there are less ways that sum is odd. So I decided to subtract from
$$9*10^4$$ which is all 5 digit numbers, the count of odd ones.
But how do I get count of the all odd ones?
Any Idea? Or maybe a better solution?