MathDB
Puerto Rico IBERO TST Problem 5

Source:

August 15, 2011

Problem Statement

Twelve balls are numbered by the numbers 1,2,3,,121,2,3,\cdots,12. Each ball is colored either red or green, so that the following two conditions are satisfied:
(i) If two balls marked by different numbers aa and bb are colored red and a+b<13a+b<13, then the ball marked by the number a+ba+b is colored red, too.
(ii) If two balls marked by different numbers aa and bb are colored green and a+b<13a+b<13, then the ball marked by the number a+ba+b is also colored green.
How many ways are there of coloring the balls?
Please remember to hide your solution. (by using the hide tags of course.. I don't literally mean that you should hide it :ninja: )