1. ## Riddles!

I thought it would be interesting to start a thread devoted to posing and dissecting riddles and brainteasers. Yeah, so I'm a pretty huge nerd.

You can most likely find the solution to any of the riddles and brainteasers people post here on the Internet, but that sort of ruins the fun now doesn't it? The first two riddles I will post here I came across surfing the Internet, matter a'fact, but you have my solemn oath I've not looked at the solutions, nor will I look for the solutions to any riddles subsequently posted in this thread before commenting upon them. Let's make that the code of conduct for this thread. Anyone who is clearly in violation of this code of conduct will have to live knowing that strangers on the Internet think he's a real fat jerk, so there.

To begin:

The Monty Hall Problem:

Suppose you're on a game show and you're given the choice of three doors. Behind one door is a car; behind the others, goats. The car and the goats were placed randomly behind the doors before the show. The rules of the game show are as follows: After you have chosen a door, the door remains closed for the time being. The game show host, Monty Hall, who knows what is behind the doors, now has to open one of the two remaining doors, and the door he opens must have a goat behind it. If both remaining doors have goats behind them, he chooses one randomly. After Monty Hall opens a door with a goat, he will ask you to decide whether you want to stay with your first choice or to switch to the last remaining door. Imagine that you chose Door 1 and the host opens Door 3, which has a goat. He then asks you "Do you want to switch to Door Number 2?" Is it to your advantage to change your choice?
The solution is here. See how closely your thinking matches!

Next is a riddle I found on an IQ test of somewhat questionable validity:

Bob is locked in a crappy dungeon with three doors, all with signs posted on them. He knows that behind one of the doors is freedom, and behind the other two doors are dragons (which will brutally maul him, because that's what they do). He also knows that at least one of the signs is telling the truth, and that at least one of the signs is lying. The signs read:

Door 1: Freedom is not behind this door.
Door 2: Freedom is not behind this door.
Door 3: Freedom is not behind the blue door.

He thinks for a second and then leaves through door number 3. Which is the blue door?
Taking this riddle at face value, it can be solved pretty quickly, but it has one rather large flaw. In order to test whether or not my thinking is solid, I'm curious to see if other members spot the same flaw.

Edit: in the name of fairness, I'll confess that people may find my issue with this riddle to be either flippant or pedantic, depending upon their assessment of my character.

Finally, the classic two guards riddle:

You stand at a fork in the road. Next to each of the two forks, there stands a guard. You know the following things: 1. One path leads to Paradise, the other to Death. From where you stand, you cannot distinguish between the two paths. Worse, once you start down a path, you cannot turn back. 2. One of the two guards always tells the truth. The other guard always lies. Unfortunately, it is impossible for you to distinguish between the two guards.

You have permission to ask one guard one question to ascertain which path leads to Paradise. Remember that you do not know which guard you're asking -- the truth-teller or the liar -- and that this single question determines whether you live or die. The question is: What one question asked of one guard guarantees that you are led onto the path to Paradise, regardless of which guard you happen to ask?
Many people are likely familiar with the proper answer, but to make this more of a challenge: imagine that you are only allowed to ask one guard one yes or no question only.

2. Originally Posted by Mycroft
Taking this riddle at face value, it can be solved pretty quickly, but it has one rather large flaw. In order to test whether or not my thinking is solid, I'm curious to see if other members spot the same flaw.

They don't define what freedom is, thats what the flaw is. Death to some people is freedom right?

3. Originally Posted by Mycroft

Finally, the classic two guards riddle:

Many people are likely familiar with the proper answer, but to make this more of a challenge: imagine that you are only allowed to ask one guard one yes or no question only.
I'd ask them the same question.... If they had ever taken a dump. I would just turn away then.....paradise is for suckers blinded by fantasy. Either path would be hell.

Reminds me of the time two Mormons came to my door. They said if I "accepted" Jesus I would get into heaven....gave me a pamphlet. It was a crudely drawn cartoon of the afterlife...had some kid petting a lion. I told them if I were "creator of the universe".....I would strike them down for such crappy illustration work. I then asked them if they would would be there (in heaven)....they said "yes". I said "fuck that".

4. I think it is quite reasonable to question the rationality and reasoning ability of Bob.

5. Two guards riddle:

This rings a vague bell even though I don't generally do such things... In any case it doesn't seem that hard:

*point to one road or the other*

*ask guard of choice "Would the other guard say that road led to heaven?"

6. Blue door? 3?

Guards: Ask one if the other tells the truth.

7. Originally Posted by ragashree
Two guards riddle:

This rings a vague bell even though I don't generally do such things... In any case it doesn't seem that hard:

*point to one road or the other*

*ask guard of choice "Would the other guard say that road led to heaven?"

When you say "the road", are you referring to the road you're pointing at or the road behind the guard you're questioning?

And no, no trick questions. Riddles with "answers" that reveal the riddle to be a trick question are by and for the sort of people who are interested enough in appearing clever to bother with such nonsense but not adequately clever to make or solve proper riddles.

Originally Posted by ygolo
I think it is quite reasonable to question the rationality and reasoning ability of Bob.
Yes, exactly! The line ought to read, "He thinks for a second and then, choosing correctly, leaves through door number 3."

As long as you take for granted that Bob isn't an imbecile, the riddle is pretty straightforward, but if you don't know that for certain it's unsolvable.

8. Originally Posted by Mycroft
When you say "the road", are you referring to the road you're pointing at or the road behind the guard you're questioning?.
That doesn't seem to materially affect the outcome... I suppose it would make more sense for it to be the one behind the guard, however.

Originally Posted by Mycroft
And no, no trick questions. Riddles with "answers" that reveal the riddle to be a trick question are by and for the sort of people who are interested enough in appearing clever to bother with such nonsense but not adequately clever to make or solve proper riddles.?.
Heh, try telling that to an ENTP, I dare you!

Yes, exactly! The line ought to read, "He thinks for a second and then, choosing correctly, leaves through door number 3."

As long as you take for granted that Bob isn't an imbecile, the riddle is pretty straightforward, but if you don't know that for certain it's unsolvable.
This seems like a badly worded question, I agree, but as it is the only possible solution I suppose it has to be taken as the one intended. I presume the person who came up with it was too busy thinking of the process to be too concerned with context. It is pretty sloppy actually...

9. Originally Posted by Mycroft
Next is a riddle I found on an IQ test of somewhat questionable validity:

blah blah Door stuff here.

Taking this riddle at face value, it can be solved pretty quickly, but it has one rather large flaw. In order to test whether or not my thinking is solid, I'm curious to see if other members spot the same flaw.
Uhm.. They're both (1&2) blue? I've never heard the first two riddles before.. the third I vaguely remember from the Labyrinth.

10. Riddle1: This has been discussed to death in another thread a few months ago.

Riddle2: As has already been stated we're going to assume that Bob chose correcty. Here is the solution:

Since we are assuming that Bob chose correctly, then let's look at the three cases for which door is blue.

Door1: If this door is blue then all three doors are telling the truth. We know that at least one is lying, so this door cannot be blue.

Door2: Same logic as Door1.

Door3: If this door is blue, then the first two doors are telling the truth and the third door is lying. Therefore this is the blue door.

Riddle3: Anyone who has seen the movie Labyrinth should be able to answer this.

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