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Lateral Puzzles » Solved Lateral Thinking Puzzles » Solved Puzzles - October 2008 » [Scottisimo] King and the three prisoners « Previous Next »

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Scottisimo (Scottisimo)
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Username: Scottisimo

Post Number: 1
Registered: 10-2008
Posted on Thursday, October 23, 2008 - 9:17 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

A king has three prisoners, he wants to let one of them go. He decides he will let the smartest go. So he sets up a fair test in order to let the smartest go.
He says he will paint a white or a red dot on their foreheads. Then place them in a room, they are not allowed to talk, or use any tricks to figure out what colour dot is on their head (like licking their finger and rubbing their forehead etc). The first one to figure out what colour dot they have can be let go.
He says if there are 2 red dots then the third dot must be white.
But in fact he paints a white dot on all 3 of them. After a while, one prisoner figures out what colour dot is on his forehead and tells the king, has the right explanantion and is let go. How did he know?

PS there is 2 answers. One is not the right one. (That 3 white dots is the only fair test).
Judgedeadd (Judgedeadd)
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Username: Judgedeadd

Post Number: 981
Registered: 9-2006
Posted on Thursday, October 23, 2008 - 10:44 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

This is not a lateral puzzle. Besides, it's an old puzzle and everyone and their dog knows this one.
Noobdogg (Noobdogg)
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Username: Noobdogg

Post Number: 656
Registered: 9-2007
Posted on Thursday, October 23, 2008 - 2:12 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

This is more of a logic puzzle mate, thanks for posting though. Also we usually prefer original lateral puzzles unless you know some interesting lateral puzzles that aren't on the "Classic Lateral puzzles" page.

Feel free to include logic in your original lateral puzzles though!
Gourami (Gourami)
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Username: Gourami

Post Number: 312
Registered: 2-2008
Posted on Monday, October 27, 2008 - 8:52 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

My dog might know this one, but I don't. What's the answer?

I mean, I can think of several ways, but none of them seem likely.
Woubit (Woubit)
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Username: Woubit

Post Number: 293
Registered: 5-2007
Posted on Tuesday, October 28, 2008 - 3:35 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Anyone seeing two red dots would know at once that his own dot must be white.

Call the prisoners A, B and C. The quickest reasoner among the prisoners (call him C) will be the first to reason as follows:

"Suppose I have a red dot. Then A (who can see a red dot on me and a white dot on B) will know after a short while that he has a white dot (otherwise B, who would be able to see red dots on both A and C, would at once have known that his own dot was white).

"B has not moved at once, and A has not moved after a short while. So I cannot have a red dot, and I had better move now."

Of course, A was not actually a prisoner at all but the King's son, who had been instructed by his father not to move in any circumstances. C was therefore in error when he drew an inference from A's inertia, and was duly executed because if there was one thing the King couldn't stand, it was a smartass.
Gourami (Gourami)
New member
Username: Gourami

Post Number: 314
Registered: 2-2008
Posted on Friday, October 31, 2008 - 10:51 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Ah, gotcha. And nice twist, Woubit.

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