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Rhondazvous · September 16, 2015 at 9:03 am

For one rep and to be induction into the Rhondazvous International Hall of Geniuses, answer the following riddle. One rep for the answer and one more rep for why that answer works.

There are two doors. Both doors are identical except behind one door is a check for 10 thousand dollars. Behind the other door is a man-eating tiger. In front of each door stands a guard. Each guard is exactly identical except one guard always tells the truth while the other guard always lies. To find out which door has the check you get to ask one guard one question. What question will you ask to which guard?

**Iroscato** · September 16, 2015 at 9:06 am

I would ask both:

"If I asked you which door leads to the check, which one would you point to?"

**Alex K** · September 16, 2015 at 9:09 am

For the sake of fairness, I have to point you to Knight000s "Intelligence Test" thread where we recently discussed this problem

Rhondazvous · September 16, 2015 at 9:13 am

(September 16, 2015 at 9:06 am)Iroscato Wrote: I would ask both:

"If I asked you which door leads to the check, which one would you point to?"

You can only ask one guard one question.

Rhondazvous · September 16, 2015 at 9:15 am

(September 16, 2015 at 9:09 am)Alex K Wrote: For the sake of fairness, I have to point you to Knight000s "Intelligence Test" thread where we recently discussed this problem

Oh, do be fair. Where is this thread? Do you have a link to it?

Exian · September 16, 2015 at 9:16 am

Aw, yeah, we've recently had this. I was looking forward to a new brain teaser, too. Thanks a lot, Rhonda!

Big Grin

**Iroscato** · September 16, 2015 at 9:18 am

(September 16, 2015 at 9:13 am)Rhondazvous Wrote:
(September 16, 2015 at 9:06 am)Iroscato Wrote: I would ask both:

"If I asked you which door leads to the check, which one would you point to?"
You can only ask one guard one question.

Bollocks.

In that case "Where would the other guard point if I asked him which door leads to the check?"

Kingpin · September 16, 2015 at 9:19 am

(September 16, 2015 at 9:03 am)Rhondazvous Wrote: For one rep and to be induction into the Rhondazvous International Hall of Geniuses, answer the following riddle. One rep for the answer and one more rep for why that answer works.

There are two doors. Both doors are identical except behind one door is a check for 10 thousand dollars. Behind the other door is a man-eating tiger. In front of each door stands a guard. Each guard is exactly identical except one guard always tells the truth while the other guard always lies. To find out which door has the check you get to ask one guard one question. What question will you ask to which guard?

The question I would ask: "If I asked what door lead to freedom, what door would the other guard point to?"

If you asked the truth-guard, the truth-guard would tell you that the liar-guard would point to the door that leads to death.
If you asked the liar-guard, the liar-guard would tell you that the truth-guard would point to the door that leads to death.
Therefore, no matter who you ask, the guards tell you which door leads to death, and therefore you can pick the other door.

Aoi Magi · September 16, 2015 at 9:22 am

(September 16, 2015 at 9:06 am)Iroscato Wrote: I would ask both:

"If I asked you which door leads to the check, which one would you point to?"

Wouldn't work as they can both show their own doors. You have to ask each guard what the other one's reply would be to which door is the correct one.

Basically

D1 - G1 - tells lie
D2 - G2 - tells truth

Assume D1 is the correct door

Ask each guard which door the other guard will show:

In case of G1(liar): G2 will point to D1 hence G1 will lie and point to D2
In case of G2(honest): Will correctly say that G1 will point to D2.

So you just have to do the opposite to both and enter D1.

This only works if you assume both guards know of each other's honesty or dishonesty.

**Iroscato** · September 16, 2015 at 9:27 am

I demand a rep for effort Tongue

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