A Number Game

Here is a set of numbered balls used for a game:

To play the game, the balls are mixed up and two balls are randomly picked out together. For example:

The numbers on the balls are added together: 4+5=9

If the total is even, you win. If the total is odd, you lose.

Here are three more sets of balls:

 

The game can be played for the total of 3 balls, 4 balls etc and for even/odd any sum or for even/odd products.