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Time for a workout!

In front of you, there are 9 coins. They all look absolutely identical, but one of the coins is fake. However, you know that the fake coin is lighter than the rest, and in front of you is a balance scale. What is the least number of weightings you can use to find the counterfeit coin?
Time for a workout!
 wantadog posted over a year ago
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Kragfan1910 said:
2.
Let me explain my reasoning.
So, I'm making the assumption you don't know the weight of the coin, that this isn't a bullion coin with a labeled "1 troy ounce" or anything along those lines.
So let's say you weigh a coin, and it comes in one half of a troy ounce, is that the real coin or the fake one? You don't know, until you weigh a second one, and it comes in at a full troy ounce, you now now that your first coin is significantly lighter, and it is therefore the counterfeit coin.
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posted over a year ago 
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So even if you weighed the counterfeit coin first, you still need a sort of bearing, or a control group before you can know which of the coins is lighter than the rest.
Kragfan1910 posted over a year ago
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Alternately, you can solve it with math, materials science, and a beaker of water. If you get lucky and weigh a coin, and it comes out at a half a troy ounce, use the beaker to find the volume, and calculate the density, then you can compare its density to the density of the material the coin should be made out of, be it copper, nickel, or silver, and see if it matches, or if it falls short and matches the density of aluminum or titanium, if you use that method, the minimum amount of weighings would be 1.
Kragfan1910 posted over a year ago
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At least, that's what my friend Kalispel says. :P
Kragfan1910 posted over a year ago
8theGreat said:
2.








I mean... not really too difficult...
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posted over a year ago 
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Hopefully the next'll be harder
wantadog posted over a year ago
Riku114 said:
Dont.

Dont weight them at all. If they look identical and the difference in weight is not so obvious that you cant tell by holding them, dont. Pretend its real and spend it.
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posted over a year ago 
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^ Smartest post here.
Kragfan1910 posted over a year ago
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^ i agree
hplover321 posted over a year ago
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