You have two coins, A and B. One is genuine, the other is fake. You also have onegenuine coin G. You don't know if the fake coin is heavier or lighter than the genuine coin. Use a balance scale one time and figure out which coin is fake.

• What we did:
  • We put A on the scale's left side
  • We put G on the right side
  • The right side of the scale went down
• What does this mean?
  • A and G are different weights
  • We know that G is genuine
  • Coin A must be the counterfeit
  • The fake is lighter than the genuine