Weighing 9 Balls Puzzle - Solution

The Puzzle:

Weighing 9 Balls
You have 9 balls, equally big, equally heavy - except for one, which is a little heavier.

How would you identify the heavier ball if you could use a pair of balance scales only twice?

Our Solution:

Divide the 9 balls into 3 groups of 3. Compare the weight of two of those groups.

The heavier group should then be obvious, it will either tip the scales, or, if the scales stay balanced, then it is the group you didn't include.

Now, choose 2 balls from this group and compare their weights, and using the same logic as before, the heavier ball will be obvious.

See this puzzle without solution
Discuss this puzzle at the Math is Fun Forum