Weighing Coins

Three outcomes per weighing

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• A balance has three outcomes, so split suspects into three equal groups.
• $n$ weighings can find one light fake among up to $3^n$ coins.
• Counting possibilities against outcomes shows what’s possible.

Steps

1. A balance has three answers
2. Split the coins
3. How many coins?
4. Four weighings
5. The classic twelve
6. Heavier or lighter?