What you see are identical gold coins, except one coin is fool’s gold and is lighter in weight then the others.  Your only tool is a simple balance scale.  What is the fewest number of times you will need to use this scale to identify the fake coin?

What was your problem-solving strategy to solve this puzzle?  Discuss . . .

Our solution:

1.  There are eight (8) coins.  Place four (4) coins on one side of the scale, and the other four (4) on the other.  Which side is lighter?  The fake coin must be in that group.

2.  Clear the scale.  Place two (2) of those coins on one side, and the other two (2) on the other.  Which side is lighter?  The fake coin must be one of those.

3.  Clear the scale.  Place one of those coins on one side, and the other coin on the other side.  Which coin is lighter?  That’s the fake coin.  You’ve used the balance scale three (3) times.

The problem-solving strategy uses the process of elimination.  Systematically, heavier coins were eliminated ultimately revealing the lightest coin.