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White Ice
New Member
5 Posts |
 Posted - 09/25/2003 : 20:58:48
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Two old guardians keep the exit of a prison. A prisoner knows that one of the guardians always tells the truth, and the other one is a liar. The prisoner can ask only a question to each guardian, but he doesn´t know who is the liar. The prisoner is in front of two doors. One of them is the exit of the prison, and the other one is the entrance of a room with two starving lions. He doesn´t know which door is the exit, but he knows that the two guardians know which door is the exit! What is the question that the prisoner should do to the honest guardian and what is the question that the prisoner should do to the lying guardian, if he wants to leave the prison?!
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My messages maybe are incomprehensible, because my knowledge regarding the English language is still precarious... |
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Tim
SFN Regular
USA
775 Posts |
 Posted - 09/26/2003 : 01:57:56 [Permalink]
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Hell, I'd probably ask for a bottle of whiskey and a good cigar.
Oh, I forgot--I quit smoking.
Then, perhaps, I'd guess I'd ask one of the guards what the other would say, and then take the other's advise?
Did I say that right? |
"We got an issue in America. Too many good docs are gettin' out of business. Too many OB/GYNs aren't able to practice their -- their love with women all across this country." Dubya in Poplar Bluff, Missouri, 9/6/2004
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ktesibios
SFN Regular
USA
505 Posts |
Posted - 09/26/2003 : 07:44:19 [Permalink]
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I think you could solve it by asking one guard "would the other guard tell me that that (indicating a door) is the door out of here?"
Suppose that the door you indicate is the exit. You ask the truthful guard. Since the lying guard would say "no", the truthful guard will say the same thing.
You indicate the exit door and ask the lying guard. Since the truthful guard would say "yes", the lying guard will tell you "no"
You indicate the lion door and ask the truthful guard. Since the lying guard would say "yes", the truthful guard will say "yes".
You indicate the lion door and ask the lying guard. Since the truthful guard would say "no", the lying guard will say "yes".
So, if you ask the question I've given, either guard will give you the same answer, which is guaranteed to be the opposite of the truth. If whichever guard you ask says "yes", the door you've indicated is the lion door and you should take the other door. If whichever guard you ask says "no", the door you indicated is the exit.  |
"The Republican agenda is to turn the United States into a third-world shithole." -P.Z.Myers |
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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
Posted - 09/26/2003 : 08:03:52 [Permalink]
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quote:
Originally posted by White Ice
What is the question that the prisoner should do to the honest guardian and what is the question that the prisoner should do to the lying guardian, if he wants to leave the prison?!
Actually, word for word, this question is based on the assumption that the prisoner already know who is the honest guardian and the lying guardian... 
But I know what you mean. What is the question you should ask guardian no1 and no2?
There are 4 possible conditions of the doors and guardians:
Question to guard no1: would guard no2 say that door1 leads to freedom?
1. If guard1=truth and door1=freedom, the answer would be: No.
2. If guard1=truth and door1=death, the answer would be: Yes.
3. If guard1=lie and door1=freedom, the answer would be: No.
4. If guard1=lie and door1=death, the answer would be: Yes.
Question to guard no2: Does door1 lead to freedom?
1. If guard1=truth and door1=freedom, No
2. If guard1=truth and door1=death, Yes
3. If guard1=lie and door1=freedom, Yes
4. If guard1=lie and door1=death, No
As you can see, the question can be resolved with boolean algebra:
the answer is = Q2 XOR inverse(Q1 XOR Q2)
provided that we ask the questions I proposed.
Edit: ktesibios, you beat me to the finish line... |
Dr. Mabuse - "When the going gets tough, the tough get Duct-tape..."
Dr. Mabuse whisper.mp3
"Equivocation is not just a job, for a creationist it's a way of life..." Dr. Mabuse
Support American Troops in Iraq:
Send them unarmed civilians for target practice..
Collateralmurder. |
| Edited by - Dr. Mabuse on 09/26/2003 08:08:15 |
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Kil
Evil Skeptic
USA
13477 Posts |
Posted - 09/26/2003 : 08:36:45 [Permalink]
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quote:
ktesibios:
I think you could solve it by asking one guard "would the other guard tell me that that (indicating a door) is the door out of here?"
quote:
Dr. Mabuse:
Actually, word for word, this question is based on the assumption that the prisoner already know who is the honest guardian and the lying guardian...
Ktesibios is correct. All that matters is that you know that one of the guardians is and one of them isn't a liar. You can only ask one guardian the question. The answer would be the same no matter which guardian you choose to question.
The question I would ask is "Which door would the other guardian choose to exit." Then I would take the opposite door, for the reasons Ktesibios explained.
This is a variation on a very old riddle. Last time I heard this riddle, it was two identical computers except one only lies and one always tells the truth, and two doors that lead to either freedom or bondage....
edited |
Uncertainty may make you uncomfortable. Certainty makes you ridiculous.
Why not question something for a change?
Genetic Literacy Project |
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furshur
SFN Regular
USA
1536 Posts |
Posted - 09/26/2003 : 09:36:22 [Permalink]
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Maybe I am missing something, but why not ask one of the guards if he has 3 eyes. You would know who is the liar and the problem is solved. And since they set up such a stupid situation I would open the exit, then reach over and open the lion door, then jump out the exit and slam the door behind me.
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If I knew then what I know now then I would know more now than I know. |
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Kil
Evil Skeptic
USA
13477 Posts |
Posted - 09/26/2003 : 12:11:56 [Permalink]
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quote:
Fursur:
Maybe I am missing something, but why not ask one of the guards if he has 3 eyes. You would know who is the liar and the problem is solved. And since they set up such a stupid situation I would open the exit, then reach over and open the lion door, then jump out the exit and slam the door behind me.
You only get one question. So, if you use it up to figure out which guard is a liar, you are on your own. No more questions....
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Uncertainty may make you uncomfortable. Certainty makes you ridiculous.
Why not question something for a change?
Genetic Literacy Project |
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Dr. Mabuse
Septic Fiend
Sweden
9688 Posts |
Posted - 09/26/2003 : 12:27:27 [Permalink]
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quote:
Originally posted by furshur
Maybe I am missing something, but why not ask one of the guards if he has 3 eyes. You would know who is the liar and the problem is solved. And since they set up such a stupid situation I would open the exit, then reach over and open the lion door, then jump out the exit and slam the door behind me.
I believe the riddle posed by White Ice is shorter than the intended original riddle, which had more rules about what questions the guards were allowed to answer.
For a nice example of the question, see the movie "The Labyrinth" with Jennifer Connelly and David Bowie. On her way to the Castle of the Goblin King Jennifer had to face this riddle.
Edit:
Maybe my memory is fuzzed up. I need to see that movie again, it's been a long while since I say it. Suddenly I get an image flashing by with the guard saying "You can't ask Us... You can only ask one of us."
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Dr. Mabuse - "When the going gets tough, the tough get Duct-tape..."
Dr. Mabuse whisper.mp3
"Equivocation is not just a job, for a creationist it's a way of life..." Dr. Mabuse
Support American Troops in Iraq:
Send them unarmed civilians for target practice..
Collateralmurder. |
| Edited by - Dr. Mabuse on 09/26/2003 12:34:32 |
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furshur
SFN Regular
USA
1536 Posts |
Posted - 09/26/2003 : 13:21:00 [Permalink]
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quote:
You only get one question. So, if you use it up to figure out which guard is a liar, you are on your own. No more questions....
Actually the original post was worded so you can ask a question of each guard. It is now obvious to me that he meant to say you can only ask one question. I would still unleash the lions. |
If I knew then what I know now then I would know more now than I know. |
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