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Weighing a Counterfeit Coin

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Weighing a Counterfeit Coin, a selection of answers from the Dr. Math archives.

Find the Heavier Coin of 12 in 3 Weighings
If there are twelve coins in a bag, one of which is either lighter or heavier than the others, find the fake coin in exactly 3 weighings AND determine if it is lighter or heavier than the others.

Finding the Counterfeit Coin (1 of 9)
One of nine coins is counterfeit and is lighter or heavier than the others. How do I locate it in three weighings only?

Finding One Coin of 12 in 3 Steps
Given a pile of twelve coins of equal size with one of a different weight, in three weighings find the unequal coin...

3 Weighings Problem
You have a balance scale and 12 balls that all look and weigh the same except one...

Use One Weighing
There are 90 genuine coins and 10 fake coins in 10 stacks with 10 coins in each stack... Using only one weighing, determine which stack contains the fake coins.

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