Monday, August 06, 2007

A Logic Puzzle.

A wise king was informed that a pie had been stolen from his kitchens, and there were only two suspects, who were now standing in front of the throne.

"I have it on good authority," said the king, "That one of you is a knight fresh from battle, and the other is a pig-farming knave. As we all know, my trusted knights can only ever tell the truth, but lowly knaves are compelled always to lie... unfortunately, I do not know which one is which, nor who stole the pie." The king pondered his predicament for a moment.

"Did you steal the pie?" the king asked the man on the left.

"No," he said.

The king turned to the man on the right. "Did you steal the pie?"

"No," said the man on the right.

The king pondered a moment more, and then turned back to the man on the left. "Is the man standing next to you a knight?"

"Yes," said the man on the left.

"Ah hah!" said the king. "I know who did it! Guards, assassinate that pie-thief!"

Which one was the knight, which the knave, and who was the pie-thief?

Click here for the answer!

The man on the right is the knight, and the man on the left is the knave. The knight stole the pie. The king knew this because the knight was wearing armor covered in blueberry residue and the knave smelt faintly of pig-shit.

An astute reader will note that the knight lied and the knave told the truth, but one hopes the astute reader would not fall for the sort of institutionalized racism for which the king was eventually deposed.


Anonymous Dad. Again. said...

That's the kind of reasoning that leads to 800 on the verbal section of the SAT. I trust you will share this insight with your students.

May I propose a different answer. IF we accept the premise of the puzzle, the three answers given are only consistent with there being two knights. The third answer can only be yes if there are two knights or two knaves. There can't be two knaves, because both answered no to stealing the pies, which would mean they both stole pies, and only one pie was stolen. Therefore both men are non-stealing knights, and the "good authority" who said that there was one knight and one knave is lying, presumably to hide his theft.

8/06/2007 7:22 PM  

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