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Originally written by Spring:

I have one (not sure if its completely right):

A man puts $50 into a bank.
Withdraws $20, leaving $30
Withdraws $15, leaving $15
Withdraws $9, leaving $6
Withdraws $6, leaving $0

$30
$15
$6
($0) +
=======
$51

Where did the extra dollar come from?

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Originally written by Khoth:

Ten prisoners are due to be executed, but a rather twisted judge gives them a chance to survive. They are all lined up in front of each other, so each prisoner can see the people in front of him but not the people behind. The executioner puts a white or a black hat at random on each one, done so that nobody can see their own hat colour. Starting at the back, each prisoner has to say either "black" or "white". If he says the colour of his hat, he is freed, otherwise he is executed. Prisoners can hear what the previous ones said.

In advance, they are allowed to come up with a strategy to save as many as possible. What should they do, and how many (on average) will survive?

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Originally written by Explode Thuryl Now:

Wait, how? I don't see how you get to 9.5.

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Originally written by Explode Thuryl Now:

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Originally written by Jumpin' Salmon:

State the color of the hat in front of "him." This means 9.5 on average will survive.

*this message sponsored by half.com*

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Wait, how? Each person can either give the guy in front of him information by stating the colour of the hat in front of him, or act on the information given to him by stating his own hat colour given to him by the guy behind him -- he can't do both. I can see how you can get up to 7.5 by having people alternate between stating the hat colour in front of them and their own hat colour, but I don't see how you get to 9.5.

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