Topical debate, moral dilemmas and quirky questions. Join fellow shareholders in civilised discussions of issues of interest
-
BeautifulSunshine
- Posts: 26721
- Joined: Tue Sep 14 2010 8:23pm
- Location: [The Finest City in the World: London]
- Has thanked: 192 times
- Been thanked: 3686 times
-
Contact:
Post
by BeautifulSunshine » Mon Sep 14 2020 7:30pm
Sarah wrote: ↑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).
Very clever the way you explained that.
[imutual Cashback Investment Club]
-
kevinchess1
- Posts: 23770
- Joined: Mon Jun 28 2010 11:02pm
- Location: Miles away from the sea
- Has thanked: 12599 times
- Been thanked: 17167 times
-
Contact:
Post
by kevinchess1 » Mon Sep 14 2020 10:44pm
Sorry Sarah but you’re wrong
Perfectly solvable with ignorant guards
The clue is in your explanation of how you work the answer out
Politically incorrect since 69
-
Sarah
- Posts: 5872
- Joined: Sat Jun 26 2010 10:01am
- Has thanked: 432 times
- Been thanked: 4446 times
-
Contact:
Post
by Sarah » Tue Sep 15 2020 5:00am
Okay, yes, poor explanation and it can also be done by asking a question that includes an inner question (e.g. "If I were to ask you 'Is this door safe?' would your answer be 'yes'?") but that feels quite cheaty as it's like asking two questions. I find the other solution of asking one guard what the other would say to be more satisfying and fair. If you permit the question-within-a-question approach then the other guard and other door don't even need to exist in the problem.
-
Chadwick
- Posts: 2436
- Joined: Mon Jul 05 2010 4:21pm
- Has thanked: 1235 times
- Been thanked: 2588 times
-
Contact:
Post
by Chadwick » Tue Sep 15 2020 12:27pm
kevinchess1 wrote: ↑Mon Sep 14 2020 1:53pm
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.
Not at all. One guard always tells the truth, the other always lies. They don't need to know this about each other. Whatever happens, one always lies and one always doesn't lie.
-
Chadwick
- Posts: 2436
- Joined: Mon Jul 05 2010 4:21pm
- Has thanked: 1235 times
- Been thanked: 2588 times
-
Contact:
Post
by Chadwick » Tue Sep 15 2020 12:33pm
Sarah wrote: ↑Tue Sep 15 2020 5:00am
Okay, yes, poor explanation and it can also be done by asking a question that includes an inner question (e.g. "If I were to ask you 'Is this door safe?' would your answer be 'yes'?") but that feels quite cheaty as it's like asking two questions. I find the other solution of asking one guard what the other would say to be more satisfying and fair. If you permit the question-within-a-question approach then the other guard and other door don't even need to exist in the problem.
Your first question "If I were to ask you..." won't work because you're only asking one guard. You don't know if they are lying or not when they answer.
By passing the information through both guards you know that one has changed the answer and one has not changed it. The answer you receive has therefore been changed once from the truth. As there are only two possible answers to the question, the other answer must be the correct one.
Think of like two light switches. One is always ON and one is always OFF. It doesn't matter which order they are in. Live electricity (the correct answer) passes through both switches and one of them turns it off, leaving the lightbulb (you) with the opposite end result (no power).
-
kevinchess1
- Posts: 23770
- Joined: Mon Jun 28 2010 11:02pm
- Location: Miles away from the sea
- Has thanked: 12599 times
- Been thanked: 17167 times
-
Contact:
Post
by kevinchess1 » Sat Sep 19 2020 10:19am
Chadwick wrote: ↑Tue Sep 15 2020 12:33pm
Your first question "If I were to ask you..." won't work because you're only asking one guard. You don't know if they are lying or not when they answer.
Me 'If I were to ask you is this the door to freedom, what would you say?'
Guard 'Yes'
This is door to freedom.
The truth telling guard will answer 'yes' because he tell the truth
The liar guard will answer 'yes' because he know he's going to reply 'no' if you ask him
Is this helpful, or do you need pictures?
Politically incorrect since 69
-
kevinchess1
- Posts: 23770
- Joined: Mon Jun 28 2010 11:02pm
- Location: Miles away from the sea
- Has thanked: 12599 times
- Been thanked: 17167 times
-
Contact:
Post
by kevinchess1 » Sat Sep 19 2020 10:22am
When I was at Junior school. last century, we did a lot of these Logic puzzles, the farmer trying to get his goods safely to market over a river, figuring out the man with a different weight in a group, various dead bodies posers and weighing out stuff when you didn't have a full range of equipment
Good times.
Politically incorrect since 69
-
Chadwick
- Posts: 2436
- Joined: Mon Jul 05 2010 4:21pm
- Has thanked: 1235 times
- Been thanked: 2588 times
-
Contact:
Post
by Chadwick » Mon Sep 21 2020 7:20pm
kevinchess1 wrote: ↑Sat Sep 19 2020 10:19am
Chadwick wrote: ↑Tue Sep 15 2020 12:33pm
Your first question "If I were to ask you..." won't work because you're only asking one guard. You don't know if they are lying or not when they answer.
Me 'If I were to ask you is this the door to freedom, what would you say?'
Guard 'Yes'
This is door to freedom.
The truth telling guard will answer 'yes' because he tell the truth
The liar guard will answer 'yes' because he know he's going to reply 'no' if you ask him
Is this helpful, or do you need pictures?
Ah, I see, a sort of double negative.
Curious to see the pictures though, since you've offered.
-
BeautifulSunshine
- Posts: 26721
- Joined: Tue Sep 14 2010 8:23pm
- Location: [The Finest City in the World: London]
- Has thanked: 192 times
- Been thanked: 3686 times
-
Contact:
Post
by BeautifulSunshine » Tue Sep 22 2020 5:57pm
Chadwick wrote: ↑Mon Sep 21 2020 7:20pm
kevinchess1 wrote: ↑Sat Sep 19 2020 10:19am
Chadwick wrote: ↑Tue Sep 15 2020 12:33pm
Your first question "If I were to ask you..." won't work because you're only asking one guard. You don't know if they are lying or not when they answer.
Me 'If I were to ask you is this the door to freedom, what would you say?'
Guard 'Yes'
This is door to freedom.
The truth telling guard will answer 'yes' because he tell the truth
The liar guard will answer 'yes' because he know he's going to reply 'no' if you ask him
Is this helpful, or do you need pictures?
Ah, I see, a sort of double negative.
Curious to see the pictures though, since you've offered.
Me too.
[imutual Cashback Investment Club]
Users browsing this forum: No registered users and 42 guests