Find even sum from a given set

Question

For a set that contains $=\{1,2,3,4,5,6,7,8,9\}$

How many times minimally do I have to randomly pick a number from the set to ensure the sum is even?

Answer 1

Remember: $$even+even=even$$ $$odd+odd=even$$ $$odd+even=odd$$

If you want to ensure the sum is even, you have to find the maximum number of picks. $$odd+even+even+even+even=odd$$ is the maximum number of picks to get odd.

So minimum of picks to ensure you have an even sum is six.