Riddle: You know that out of your 9 golf balls there is one that is lighter than the others. But, the light ball is to samll a difference for the "hand balance!" You're in luck, the course you're at has a scale, but you can only afford to use it 2 times. How do figure it out?
Answer: STEP 1: Divide it into sets of three. If you put one set on either side, it'll either equal the same, or you'll see which set is lighter. Either way, you narrow it down to three balls.
STEP 2: put two of the balls on the scale. If they're equal, the last ball is deffective, but if not, the scale will tell you which one is lighter.