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Riddle
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Just a short and simple riddle

There are 10 black hats, and each black hat is filled with 10 gold coins, with one hat filled with 10 fake coins. Therefore there are 9 hats filled with 10 gold coins and 1 hat filled with 10 fake coins. Each gold coin weighs 100g while each fake coin weighs 90g.

A weighing scale will be given to you. You are allowed to remove the coins from the hats to be weighed, but you only have one chance to weigh the coins before you have to determine which hat contains the fake coins. How will that be done?

Posted on: 2009/1/10 19:13
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Re: Riddle
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Keep track of the weight as you empty the hats one by one? The hat that does not add 1kg to the total depicted on the weighing scale is the hat with fake coins.

Posted on: 2009/1/10 20:15
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Re: Riddle
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let me add that you cant see the weight on the weighing scale until you are done removing the coins from the hats on to the weighing scale.

But if you could see the weight while you remove the coins then that is absolutely right

Posted on: 2009/1/11 3:54
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Re: Riddle
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Well, the other option would be to pour nitric acid on the coins; the coins that don't hold to the acid test are the fake ones.

Or, assuming the fake coins are made out of non-aluminum materials, then hold a magnet next to the hats and see which attracts the coins?

I think I have just made a simple solution extremely frustratingly complicated.

Posted on: 2009/1/11 20:19
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Re: Riddle
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I'm clueless. *waits for the answer*

Posted on: 2009/1/12 0:01
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Re: Riddle
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Toss the coins to the air, "FREE COINS, ANYONE?!"

Posted on: 2009/1/12 1:08
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Re: Riddle
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Take 1 coin out of the first hat then 2 from the 2nd and so on until you remove 10 coins from the 10th hat.
In doing so you are removing a total of 1+2+3+4+5+6+7+8+9+10=55 coins
If all the coins were real the expected weight would be 55 x 100g=5500g
Knowing that one of the hats has fake coins which is 10g less heavy than the real coins, you can work out which is it by how short the final weight of the coins are compared to the real expected weight.
eg: If you get 5450g its 50g short of the real expected weight. Therefore the 5th hat must have the fake coins

Posted on: 2009/1/12 7:14
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Re: Riddle
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It took a while, but I think I get it; so following that logic, if I'm 60g short, it has to be the 6th hat, am I right? Clever.

Posted on: 2009/1/12 9:25
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Re: Riddle
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Thats correct!

Here's another simple puzzle.

There is a pond in the middle of a jungle. In it lives a water lilly which doubles in amount every 24 hours. If it takes the water lilly 60 days to completely cover the surface of the pond, how many days will it take to cover half the surface?

Posted on: 2009/1/12 10:32
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Re: Riddle
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30 Days?

Posted on: 2009/1/12 10:38
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