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# that 2 guards 2 doors puzzle

i cant work it out,even if you ask what the solutionn says,not normally thick but it stumped me.

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i cant work it out,even if you ask what the solutionn says,not normally thick but it stumped me.

Basically you have to have a trick question where the answer is the same be it a lie or truth, as if you ask the liar a question, they have to lie so if the question is asking about a lie, then the lie is the truth.

John and Bill are standing at a fork in the road. You know that one of them is a knight and the other a knave, but you don't know which. You also know that one road leads to Death, and the other leads to Freedom. By asking one yes/no question, can you determine the road to Freedom?

There are several ways to find out which way leads to freedom. One alternative is asking the following question: "Will the other man tell me that your path leads to freedom?"

If the man says "No", then the path does lead to freedom, if he says "Yes", then it does not. The following logic is used to solve the problem.

If the question is asked of the knight and the knight's path leads to freedom, he will say "No", truthfully answering that the knave would lie and say "No". If the knight's path does not lead to freedom he will say "Yes", since the knave would say that the path leads to freedom.

If the question is asked of the knave and the knave's path leads to freedom he will say "no" since the knight would say "yes" it does lead to freedom. If the Knave's path does not lead to freedom he would say Yes since the Knight would tell you "No" it doesn't lead to freedom.

The reasoning behind this is that, whichever guardian the questioner asks, one would not know whether the guardian was telling the truth or not. Therefore one must create a situation where they receive both the truth and a lie applied one to the other. Therefore if they ask the Knight, they will receive the truth about a lie; if they ask the Knave then they will receive a lie about the truth.

Edited by:"ryouga" 20th Mar 2011You ask guard one "If I ask guard 2 which door is safe what would he say?"

If guard 1 is the liar he will lie that the other guard would tell you door 1. If he is the truthful one he will tell you that the other guard will tell you door 1. Either way you choose the door they don`t mention.

Genius

Original Poster

yes but if both say door 1 which is the liar

If I ask guard 2 which door is safe what would he say

as he has to lie he would say door one,if i then ask guard 2 the same question (he has to tell the truth and say door one

Original Poster

the liar would say yes therefore the true guy also has to say yes.

Banned

so basically the idea is that you ask one of them will the other person say their path leads to freedom.

and you do the opposite. this is because a truth and a lie equals a lie.

say the truth teller is in front of freedom and the liar is in front of death.

ask either one will the other say their path leads to freedom?

if you asked the liar he knows the truth teller is in front of freedom and so the truth teller would say "yes" so the liar says "No".

if you asked the truth teller as he knows the liar is in front of death the liar will say "Yes" and so the truth teller will say "yes".

if the liar was in front of freedom the same situation applies. just this time the truth teller would say no and the liar would say yes.

hope this helps

what colour is your hair

what is your date of birth

what is your name

Original Poster

that is genius you only need to ask one person to get the right answer.

Banned

Nope, because they can only answer yes or no.

Also, even if you establish which one is the liar you don't know which one is infront of freedom and which one is infront of death.

Banned

No,iz it because im'z thick :-/

Banned

dude I wrote post 12 for you... you kept bumping the thread so i wrote that explanation.

Original Poster

ok lets break this down in simple terms

evil guards hell and can only lie thats the left door

good can only tell the truth thats the right door

lets make left bad and right good

question

left does right guard the door to heaven ,left answers no

right does left guard the door to heaven right answers no

from here how do we say which side is lying?????????????

Banned

you ask the guard what the other guard is going to say.

truth + lie = lie so you go with the opposite of what the guard you asked has said.

THE END.

Original Poster

im the devil and guarding hell and can only lie

ask me a question

Banned

is the other guard guarding hell?

Original Poster

Banned

the other guard (angel or whatever) is going to say "No" because they are guarding heaven

since you're the devil you're going to lie about what they say so you say "Yes" that the other guard (the angel) is guarding hell.

since i know that there is a lie involved no matter which guard I ask... I go with the opposite to what the guard i ask tells me.

so I know that the other guard is guarding heaven.

THE END?

Original Poster

Banned

So I go past the other guard as i know they are guarding heaven.

Original Poster

Original Poster

Banned

do you understand how the solution works now?

or do you want to try it again but this time you be the angel?

Original Poster

Original Poster

Banned

ok lets say you're the angel but we'll keep everything else the same. (devil is guarding hell)

so I ask you "is the other guard going to say they are guarding hell"

the angel knows that the devil is going to say "no" so the angel tells the truth and says "no" that the devil is going to say no they are not guarding hell

but because i know one of them is lying i choose the opposite

Banned

I made a mistake here... the solution is to ask the guard you are speaking to that the OTHER guard is going to say.

post 26 and 34 from there is what happens:

Original Poster

Banned

it's not an oxymoron

Banned

Original Poster

1=god truth heaven

2=bad lie hell

1:if i ask 2 if he is guarding the door to heaven what would he say,he knows 2 can only lie therefore he has to say "yes" because thats the only answer 2 can give

2:if i ask 1 are they are guarding the door to heaven he can only say no as he has to answer untruthfully

it would work like that good would give a wrong answer because he has to say what bad says making hhis answer correct in hindsight.

still think its a bit dodgy tho

Original Poster