How many weighings of a balance scale are needed
to find a lighter counterfeit coin among four coins? . . . . Two
Describe an algorithm to find the lighter coin using this number of weighings.
Weighing #1: Weigh two coins against the other two.
. . The pan that is higher contains the lighter coin.
Weighing #2: Weigh the coins from the higher pan against each other.
. . The coin in the higher pan is the counterfeit.
With two weighings, the lighter coin can be found from among nine coins.
Can you determine the procedure?