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There is a prisoner who will be executed, but there is a rule in the kingdom that says, "the prisoner will be given a bag containing a white paper and a black paper. If the prisoner is lucky enough to draw the white paper, he will be released; otherwise he will be executed."

The person preparing the bag hated the prisoner, so he actually put 2 pieces of black paper into the bag instead of 1 black and 1 white. And the prison guard saw this and told the prisoner about it.

Can the prisoner overcome this situation and how? (and be actually released)

Pulling both pieces out of the bag will merit execution.

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  • $\begingroup$ Would it be too lateral-thinking to pull both pieces of paper out of the bag and simply expose the perfidy? $\endgroup$ – Trevor Powell May 31 '15 at 2:59
  • $\begingroup$ Why can't we just say what we were told by the prison guard? $\endgroup$ – BCLC May 31 '15 at 12:14
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    $\begingroup$ How do we the prisoner know the prisoner guard is telling the truth? $\endgroup$ – BCLC May 31 '15 at 12:54
  • $\begingroup$ Why is the prisoner not allowed to verify the papers after to ensure the bag is not rigged? $\endgroup$ – BCLC May 31 '15 at 12:59
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The prisoner could

The prisoner picks one at random but crumple it up so nobody sees. He claims that this was the on he picks, and does something to destroy the paper forever, like eat it. The guards look in the bag to see the black slip of paper, and concludes that the paper he picked must have been the white slip of paper.

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  • $\begingroup$ yes your answer is very close to an answer I read long time ago... for that answer you can see my answer on this page $\endgroup$ – 太極者無極而生 May 30 '15 at 20:27
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    $\begingroup$ @太極者無極而生 Isn't this the same as Spencerkatty's answer, which was earlier? $\endgroup$ – Rand al'Thor May 30 '15 at 21:25
  • $\begingroup$ I do promise I didn't look at his answer while writing mine, but I do agree with you, and I thought it was strange that he awarded mine, but you have to think about one thing: "What is fair?" Why is it fair that anyone gets the accepted answer? Just because I typed mine slower, and was stopped by the Captcha, shouldn't mean that he gets the accepted answer instead of me, and vice versa. Who should get it, and is it fair to anybody that participated on this question? $\endgroup$ – Xandawesome May 30 '15 at 21:29
  • $\begingroup$ I guess it just depends on the quality of the answer. $\endgroup$ – Xandawesome May 31 '15 at 2:17
  • $\begingroup$ What if the prison guard lied and there are 2 whites instead? :P $\endgroup$ – BCLC May 31 '15 at 12:55
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The answer that comes to my mind is:

Draw one piece of paper
Before anyone sees it destroy it somehow (burn it, eat it, throw it out the window, whatever...)
Then show that the paper remaining in the bag is black and so therefore he must have drawn the white one.

Everybody gets away safe without anyone getting in trouble for trying to overcome the kingdom's strange rules.

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  • $\begingroup$ of your 3 actions, the first one is hard to do as how do you have such device to take such action? The third one is risky as what if they just go outside or go downstairs... $\endgroup$ – 太極者無極而生 May 30 '15 at 20:37
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    $\begingroup$ @太極者無極而生 I was just listing different ways that may or may not be available to destroy the paper. Say, for example, the room they are in is lit by torches (it sounds like an old-world kingdom without electricity with these rules they have) or maybe it's really windy outside and the paper blows away really quickly. Just thinking of different possibilities. $\endgroup$ – Spencerkatty May 30 '15 at 21:19
  • $\begingroup$ What if the prison guard lied and there are 2 whites instead? :P $\endgroup$ – BCLC May 31 '15 at 12:56
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Similar to MisterEman22's answer, who beat me to the punch.

The prisoner suggests, "For my last request, how about you pull out a piece of paper instead, and I choose the other paper in the bag? I simply ask because I hate touching paper. If you pull black, that means the paper in the bag is white, so I go free. If you pull white, I die. Surely this doesn't improve my chances, so there is no reason to deny me this request."

The king cannot say no without appearing suspicious, so he agrees, and the prisoner lives.

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He could:

Before drawing, propose the rule that instead of being released if he draws the white paper, he will be released if he draws the black paper. Since there should be the same probability that he will draw black as white (50/50) there is no reason for the government/rulers to disallow this change of rules. He then draws black and is allowed to live.

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@Xandawesome's and @Spencerkatty's answer is very close to mine, and it is like this:

The prisoner takes a paper, and if it is small, just hide it in the palm and if too big, crumble it and hide in his hand, and he declares "Almighty God, I choose this one, and may it be white!", and then he eats/swallows the paper. Now they cannot kill him to get the paper out, as he is supposed to be released if the paper is white, and they or the prisoner will suggest, which paper did he choose, let's take a look at what's left in the bag and we will know... and it is a black one, so the conclusion is that he is lucky to pick the white one

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