Don,t know if this puzzle has been done before,,,,a house has two opposite doors one leads to safety,the other leads out over a mountainous drop,inside the house is 2 boys,1 always tells the truth 2nd always tells lies,but you don,t know which is which,you ask one question to find out the correct door to go to safety,what is the solution,mike

I know a form of this puzzle, but not this one.

A double negative is a positive.

"If I asked you if this is the door that leads to
safety, would you answer 'yes'?"

The one that tells the truth would say ,,,yes but if you asked the other he would say no,,,but you don't know which tells the truth or lies,he he

Let's say the door does lead to safety.

If I asked the truth-teller if it led to safety,
he would answer "yes." So when I ask him, "If I
asked you if this is the door that leads to safety,
would you answer 'yes'?", he would have to answer
"yes."

If I asked the liar if it lead to safety, he
would answer "no." So when I ask him, "If I
asked you if this is the door that leads to safety,
would you answer 'yes'?", he would have to
answer "yes."

Similarly, if the door didn't lead to safety,
both liar and truth-teller would have to
answer my question with a "no."

A negative times a positive
or a positive times a negative
is negative.

I could also ask, "If I asked the
other boy if this is the door that
leads to safety, would he answer
'no'?"

A "yes" answer to this question
means the door does lead to
safety.
A "no" answer means it doesn't
lead to safety.

Hi stan,i had to go over and over your answer many times,the answer is basically the same just another way of putting it,,,you want to go through the door to safety so you ask boy A what B will say,whatever the answer you take the OTHER door,mike

Aside from the grammar problem...

First the boys are infants, and unable to talk. Then, sadly the house being on fire and full of smoke, it was a bit too noisy to hear any reply they gave. Oh well. Next.

So sorry I should have said (are),,,,,,,,,,,,,jonathan,hay man wot iz de problem wid yew (liten up, yoo no wot i,m sayin) so long has yoo understan wot I say,yoo ave to learn to ave respeck for uders hoo are not has clever has yoo,we not alls tawk wiv a plum in de mout,,,, and not be condescending, being courteous costs nothing,lighten up,mike

Honestly your honor, I was in this house with two boys and I was just trying to get them to tell me which door I could use.

Find a copy of the Dr. Who episode "Pyramid of Mars" or the film "Labirynth," the puzzle appears in both of those.
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Ask either of the people... if I asked HIM (pointing to the other child) if this (Door A) was the safe door, what would he say?

If the boy you ask says the other boy would say "yes," (the door is safe) the door is the dangerous one and should be avoided.


Here's how I think it works out;


If you ask the liar, he knows the other boy would say "no" but he'll lie and say the other boy would say "yes."

If you ask the truth teller, he knows the other boy would lie about the status of the door so he will say "yes."

Did I break the thread?

Not broken though a classic re-chafe.

Mandrake,your answer was correct,stan had already guessed it,mike

Shoot