Identifying a Counterfeit Coin Using a Simple Balance: A Mathematical Challenge

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  • Thread starter Thread starter Chikawakajones
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Discussion Overview

The discussion revolves around a mathematical challenge involving the identification of a counterfeit coin among twelve coins using a simple balance scale within three weighings. Participants explore various methods and assumptions related to the problem, including the nature of the counterfeit coin and alternative approaches to the challenge.

Discussion Character

  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant suggests dividing the twelve coins into two stacks of six and weighing them to identify the lighter stack, then further dividing the lighter stack to isolate the counterfeit coin.
  • Another participant questions the limitation of the problem to twelve coins, proposing that it is possible to identify a counterfeit coin among 27 coins in three weighings if the counterfeit is known to be lighter.
  • A different viewpoint is raised regarding the initial problem's interest, suggesting it would be more intriguing if the counterfeit coin's weight difference was unknown.
  • One participant proposes an alternative method inspired by Archimedes, suggesting that measuring water displacement could be used to identify the counterfeit coin.
  • Another participant notes a basic assumption that all coins have the same volume, which would affect the water displacement method, and emphasizes the need to find the counterfeit coin within three measurements.

Areas of Agreement / Disagreement

Participants express differing views on the problem's parameters and methods, with no consensus reached on the best approach or assumptions regarding the counterfeit coin's weight.

Contextual Notes

There are assumptions about the coins' weights and volumes that are not universally accepted, and the discussion includes unresolved mathematical steps regarding the proposed methods.

Chikawakajones
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You may have heard that money is the evil of this world, but as number devils it gives us the task to create math problems in the business world.
So here is the next problem. :rolleyes:

You have twelve coins,
One of which is counterfeit and weighs less than the legal ones.

How can you use a simple balance, three times to determine which coin is counterfeit :confused: ?
 
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Help Me Please
 
Chikawakajones said:
Help Me Please

Divide the 12 coins into two stacks of six and weigh them on the balance. The stack with the counterfeit coin will be lighter.

Now take the lighter stack of 6 and divide it into two stacks of three and weigh them on the balance. Again, the stack with the counterfeit coin will be lighter.

You figure it out from there.
 
Why only 12?

You could find one ball in 27 in three weighings if you know it's light.

Could you find one light ball out of 3 in one weighing?
What about one light ball out of 9 in two?
 
The initial problem is more interesting if you do not know that the bad coin is lighter, only that it differs in weight.
 
a better way would be to do what archimedes did and put each coin in the same amount of water to test how much water they displace
 
A basic assumption would be that each coin has the same volume, thus will displace that same amount of water. Also you must find the coin in 3 measurements.
 

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