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Re: Giraffe Test
Virtual1 #11518 08/20/10 06:08 PM
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grelber Offline OP
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Jawohl! smile

Re: Giraffe Test
Virtual1 #11520 08/20/10 08:48 PM
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Originally Posted By: Virtual1
The test isn't very fair. Its only purpose appears to be to make people feel dumb wink


Ok, try this one. (I hope I get all the details!)

You're hiking in a remote wilderness when you come to a fork in the road. Each of the two roads leads to a village, and each has a sentry posted at the fork. You have only the following information:

One road leads to a village populated by cannibals. They will certainly kill you. The other village is populated by friendly people who will feed and house you. You also know that one of the sentries always tells the truth, and one of them always lies. You are allowed to ask one of the sentries one question only. What question should you ask, and of which sentry, in order to insure that you choose the road to the friendly village?

Now, if I could only remember the question....

Hint: Think about what you don't know.

I'll be back in a month or so. wink

Re: Giraffe Test
Gregg #11523 08/20/10 10:06 PM
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Originally Posted By: Gregg
....and of which sentry...

I don't understand this part. If I know which sentry is which, don't I also know which road to take?

Am I missing something?

ryck

Last edited by ryck; 08/20/10 10:06 PM.

ryck

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Re: Giraffe Test
Gregg #11525 08/20/10 10:13 PM
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You ask either sentry... If I were to ask you which road leads to the friendly village what would you answer?


The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
Re: Giraffe Test
artie505 #11527 08/20/10 10:47 PM
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Originally Posted By: artie505
You ask either sentry... If I were to ask you which road leads to the friendly village what would you answer?


Not quite. If the sentry answering was the liar, "se" would tell you the wrong road, but how do you know that sentry is lying? If it is the truthful sentry, how would you know to trust "se"?

The hint really applies to the above explanation.

Re: Giraffe Test
ryck #11528 08/20/10 10:48 PM
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Originally Posted By: ryck
Originally Posted By: Gregg
....and of which sentry...

I don't understand this part. If I know which sentry is which, don't I also know which road to take?

Am I missing something?


No, you've just stumbled over the hint. And, you've ferreted out a universal truism: you're just as likely to be supplied with irrelevant information as to be not supplied with enough.

Re: Giraffe Test
Gregg #11530 08/20/10 11:27 PM
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You ask either sentry, "if I ask the other sentry whether he is guarding the road leading to the friendly village, what will he answer?"

If the other sentry is guarding the road leading to the friendly village, the sentry you ask will say, "no," regardless of whether he or the other sentry is the truth teller. If not, the answer will be "yes" in either case.



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Re: Giraffe Test
dkmarsh #11531 08/21/10 12:04 AM
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Originally Posted By: dkmarsh

You ask either sentry, "if I ask the other sentry whether he is guarding the road leading to the friendly village, what will he answer?"

If the other sentry is guarding the road leading to the friendly village, the sentry you ask will say, "no," regardless of whether he or the other sentry is the truth teller. If not, the answer will be "yes" in either case.


Right, but back to being picky... you can't ask the other sentry anything, so framing the question that way is, what... awkward? (can't find the word I need) Maybe, "If I could ask the other sentry..." or "If you asked the other sentry..."

Anyway, the key is that you don't know which sentry to ask, so that's irrelevant. Your question has to be posed in such a way that you're able to determine the correct road to take without knowing if the sentry is lying or not, as the above question is so posed.

Now, dk, had you heard this or another similar riddle before?? Fess up! (You too, Artie. Just didn't quite remember the correct answer there, but close!)

Re: Giraffe Test
Gregg #11533 08/21/10 05:37 AM
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Originally Posted By: Gregg
Originally Posted By: artie505
You ask either sentry... If I were to ask you which road leads to the friendly village what would you answer?


Not quite. If the sentry answering was the liar, "se" would tell you the wrong road, but how do you know that sentry is lying? If it is the truthful sentry, how would you know to trust "se"?

The hint really applies to the above explanation.

Sorry, Gregg, but my answer is correct.

By phrasing the question "If I were to ask you" you trap the lying sentry... If you ask hir the question directly se'll lie, but in answering the indirect question se'll lie about the lie.

The truthful sentry, on the other hand, will answer truthfully in response to both the direct and indirect questions.

> [...] how would you know to trust "se"?

That's "hir." grin

Edit: Yep... This is not a new one on me, and, as I recall, the answer I heard way back when was somehow different from what I've posted, but I stand by my post, nonetheless.

Last edited by artie505; 08/21/10 06:05 AM.

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
Re: Giraffe Test
artie505 #11538 08/21/10 12:53 PM
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Originally Posted By: artie505

By phrasing the question "If I were to ask you" you trap the lying sentry... If you ask hir the question directly se'll lie, but in answering the indirect question se'll lie about the lie.

The truthful sentry, on the other hand, will answer truthfully in response to both the direct and indirect questions.


Ok, I'll buy that. Much more subtle. You're really depending on those sentries to be intellectual heavyweights though. I think the other way would be safer! wink

Re: Giraffe Test
Gregg #11541 08/21/10 05:40 PM
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Originally Posted By: Gregg
Right, but back to being picky


I can do picky too. The assumption that the sentries know whether the other sentry is a liar isn't entirely safe.


I work for the Department of Redundancy Department
Re: Giraffe Test
Gregg #11544 08/21/10 07:47 PM
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> You're really depending on those sentries to be intellectual heavyweights though.

Nope! I'm merely depending on them to do their thing, whether it be telling the truth or lying.


The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
Re: Giraffe Test
artie505 #11545 08/21/10 09:13 PM
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Exactly.

(And, by the way, it's another oldie but goodie, having graced many a logic and/or philosophy class.)

Re: Giraffe Test
artie505 #11551 08/23/10 12:26 AM
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Originally Posted By: artie505
> You're really depending on those sentries to be intellectual heavyweights though.

Nope! I'm merely depending on them to do their thing, whether it be telling the truth or lying.


Well, the scenario is that it's a remote wilderness. Perhaps the sentries aren't educated enough to know the difference between a direct and an indirect question. The other question, as you point out, assumes each sentry knows the same things that you know about them. Unless it's the first day on the job for one or both of them, I'd say that's a good assumption. But, I'm just being picky right back at ya. wink

Re: Giraffe Test
Gregg #11552 08/23/10 04:12 AM
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Originally Posted By: Gregg
Perhaps the sentries aren't educated enough to know the difference between a direct and an indirect question.

Understanding the question I posed requires no education at all, merely an understanding of the language in which it was posed.


The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
Re: Giraffe Test
artie505 #11557 08/23/10 11:43 PM
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Easy for you to say. You're well educated. Those that aren't don't understand the language they speak very well. That's why lawyers don't ask them indirect or compound questions. Or, when they do, they're forced to restate and break down the question into smaller bites. Classic case of that when I was on a jury: the lawyer apologized and then led the witness on a three or four question journey to arrive at the same destination as his original question. I know you're going to stand by your assertion. And I'm going to stand on my position that it is incorrect. Have a nice day.

Re: Giraffe Test
Gregg #11564 08/26/10 01:00 AM
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wink


The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
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