Topical debate, moral dilemmas and quirky questions. Join fellow shareholders in civilised discussions of issues of interest
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xxxraichxxx
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by xxxraichxxx » Thu Sep 10 2020 6:35pm
You are a prisoner in a room with 2 doors and 2 guards.
One of the doors will guide you to freedom and behind the other is a hangman. You don't know which is which. One of the guards always tells the truth and the other always lies. You don't know which one is the truth-teller or the liar either. You have to choose and open one of these doors, but you can only ask a single question to one of the guards. How do you avoid the hangman?
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Sarah
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by Sarah » Thu Sep 10 2020 7:15pm
That's a classic puzzle that many people will have seen before; it's equivalent to the 'Knights and Knaves' problem 'Fork in the road' as described here:
https://en.wikipedia.org/wiki/Knights_a ... n_the_road
This version of the puzzle was further popularised by a scene in the 1986 fantasy film, Labyrinth, in which the protagonist finds herself faced with two doors with guardians who follow the rules of the puzzle. One door leads to the castle at the centre of the labyrinth, and one to certain death. It had also appeared some ten years previously, in a very similar form, in the Doctor Who story Pyramids of Mars.
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BeautifulSunshine
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by BeautifulSunshine » Thu Sep 10 2020 7:37pm
Sarah wrote: ↑Thu Sep 10 2020 7:15pm
That's a classic puzzle that many people will have seen before; it's equivalent to the 'Knights and Knaves' problem 'Fork in the road' as described here:
https://en.wikipedia.org/wiki/Knights_a ... n_the_road
This version of the puzzle was further popularised by a scene in the 1986 fantasy film, Labyrinth, in which the protagonist finds herself faced with two doors with guardians who follow the rules of the puzzle. One door leads to the castle at the centre of the labyrinth, and one to certain death. It had also appeared some ten years previously, in a very similar form, in the Doctor Who story Pyramids of Mars.
Very knowledgeable of you Sarah.
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blythburgh
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by blythburgh » Fri Sep 11 2020 7:42am
Sarah wrote: ↑Thu Sep 10 2020 7:15pm
That's a classic puzzle that many people will have seen before; it's equivalent to the 'Knights and Knaves' problem 'Fork in the road' as described here:
https://en.wikipedia.org/wiki/Knights_a ... n_the_road
This version of the puzzle was further popularised by a scene in the 1986 fantasy film, Labyrinth, in which the protagonist finds herself faced with two doors with guardians who follow the rules of the puzzle. One door leads to the castle at the centre of the labyrinth, and one to certain death. It had also appeared some ten years previously, in a very similar form, in the Doctor Who story Pyramids of Mars.
But still a bit of fun and you something to thing about
P.S. The answer is .... You need to think about it very carefully before asking your question
Keep smiling because the light at the end of someone's tunnel may be you, Ron Cheneler
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Chadwick
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by Chadwick » Sun Sep 13 2020 5:29pm
Ask guard A: What would guard B say is behind door A.
Whatever the answer, the opposite is behind door A.
I take no particular credit for 'solving' this riddle. It's a very old one and I just happen to know the answer.
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Chadwick
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by Chadwick » Mon Sep 14 2020 10:37am
As an aside, on the Rpoints forum - which used the same underlying message board code I think - there was a way of writing something so that it would be invisible until you highlighted it. Anyone know if that's possible on this forum?
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Sarah
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by Sarah » Mon Sep 14 2020 11:13am
The usual way on most forums is [SPOILER]something hidden[/SPOILER] but it's not supported here.
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blythburgh
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by blythburgh » Mon Sep 14 2020 12:01pm
Chadwick wrote: ↑Mon Sep 14 2020 10:37am
As an aside, on the Rpoints forum - which used the same underlying message board code I think - there was a way of writing something so that it would be invisible until you highlighted it. Anyone know if that's possible on this forum?
It works as it tried highlighting the empty bit and got the full post and the answer is X
Keep smiling because the light at the end of someone's tunnel may be you, Ron Cheneler
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kevinchess1
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by kevinchess1 » Mon Sep 14 2020 1:53pm
Chadwick wrote: ↑Sun Sep 13 2020 5:29pm
Ask guard A: What would guard B say is behind door A.
Whatever the answer, the opposite is behind door A.
I take no particular credit for 'solving' this riddle. It's a very old one and I just happen to know the answer.
I’m not convinced you have ‘solved’
Your answer assumes that the guards know that the other one lies/tells truths
So, same riddle but the guards know nothing about each other.
Politically incorrect since 69
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Sarah
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by Sarah » Mon Sep 14 2020 2:46pm
The guards need to be fully knowledgeable about each other and their situation. It can't be solved otherwise - the key to the problem is obtaining 2 pieces of information using 1 question, which you can't hope to do by asking 1 question of 1 guard if each guard only knows 1 piece of information (i.e. their own).
Last edited by
Sarah on Mon Sep 14 2020 7:43pm, edited 2 times in total.
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