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Subject: "12 Coins Puzzle!?"     Previous Topic | Next Topic
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Hogan
guest
Dec-17-03, 02:41 PM (EST)
 
"12 Coins Puzzle!?"
 
   I thought the real solution to this problem was a binary search like scenario?

E.g. for all coins where x is a valid coin and y is the fake one, do this:

xxxxxx vs xxxxxy (put 6 coins on each side, pick the lighter side)
xxx vs xxy (pick the lighter side and divide the coins)
x vs x (then weigh two of the remaining three coins)

SO, if the two coins weighed are the same, then the odd coin out is the fake, else it is the lighter of the two.

and we know the fake coin.

Or are we just looking for a mathematically induced solution.


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alexb
Charter Member
1150 posts
Dec-17-03, 02:46 PM (EST)
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1. "RE: 12 Coins Puzzle!?"
In response to message #0
 
   >I thought the real solution to this problem was a binary
>search like scenario?

What is a real solution?

>Or are we just looking for a mathematically induced
>solution.

What is mathematically induced? Something like Newton Laws?


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Hogan
guest
Dec-17-03, 09:46 AM (EST)
 
2. "RE: 12 Coins Puzzle!?"
In response to message #1
 
   Sorry about the ambiguities i've introduced.

By 'real' I mean one of the first solutions proposed.
By mathematically induced I mean a solution comprised of (or proved from) mathematical formulae and properties.


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alexb
Charter Member
1150 posts
Dec-18-03, 10:07 AM (EST)
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3. "RE: 12 Coins Puzzle!?"
In response to message #2
 
   >Sorry about the ambiguities i've introduced.

That's OK. Clearly, no offense was intended, nor any was taken.
>
>By 'real' I mean one of the first solutions proposed.

No one solution os more 'real' than the next. I think solutions to a problem may be categorized as more or less useful, or, say, more or less elegant. One solution is more useful than another if it's less ad hoc, i.e. if it applies to a wider range of problems. Whether a solution is elegant is often in the eyes of a beholder. I personally think that Jack Wert's solution is the most elegant and also find it the most useful, because of the immediacy with which it extends to a larger number of coins.

>By mathematically induced I mean a solution comprised of (or
>proved from) mathematical formulae and properties.

Mathematics is more about formal reasoning than about using formulas. Math language is just a tool that helps make a problem more manageable.

Jack Wert's solution does not use any formulas, but only common sense. However, the reasoning is quite formal. So I would not deny it the mathematical nomenclature.


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Jack wert
guest
Dec-20-03, 10:07 PM (EST)
 
4. "RE: 12 Coins Puzzle!?"
In response to message #0
 
   >I thought the real solution to this problem was a binary
>search like scenario?
>
>E.g. for all coins where x is a valid coin and y is the fake
>one, do this:
>
>xxxxxx vs xxxxxy (put 6 coins on each side, pick the
>lighter side)
What do you do next if the odd weight coin is heavier, and the lighter side is all good coins. Your solution appears to be only for a situation wherein the odd coin is lighter.

I think you will find that ternary solutions are the only approach that provides in the desired result.
> xxx vs xxy (pick the lighter side and divide the
>coins)
> x vs x (then weigh two of the remaining three
>coins)
>
>SO, if the two coins weighed are the same, then the odd coin
>out is the fake, else it is the lighter of the two.
>
>and we know the fake coin.
>
>Or are we just looking for a mathematically induced
>solution.
>


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