 If they weigh different, you know that the heavier ball is in the scale that goes down the further. So now you have a set of three balls of which you know that the heavier ball is one. And then you do the same thing by weighing one ball against another ball of those three balls. Do the same thing again. If they weigh the same, then the odd ball out is the one that remains. And if they weigh different, whichever one is the heavier is the odd ball out. Okay.