Bite-Size Physics

For the first weighing, she needs to put three coins on one side of the balance, three coins on the other side and leave three coins off the scale. She knows that the cursed coin is a little heavier. So if one side of the balance dips, she knows the coin is on that side. If both sides balance, than the coin is in the set of coins left off the scale.

For the second weighing, she needs to take whichever batch of coins she found to be heavier. She puts one coin on one side of the balance, one coin on the other, and leaves one coin off the scale. If the balance tips, that’s the cursed coin. If the balance is even, the cursed coin is sitting off the scale.

So she finds the cursed coin in the nick of time and runs, runs, runs!

Good job, Phyllis!

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