Prove that given any set of $17$ integers, there exist nine of them whose sum is divisible by $2.$
Prove that given any set of $17$ integers, there exist nine of them whose sum is divisible by $2.$
How about demonstrating an exception? A set of seventeen 3's. You did say "any" set.
3 3 3 3 3 3 3 3 3
3 3 3 3 3 3 3 3
Choose and add up any nine of them. The total is 27. Not divisible by 2.