You are trapped in a prison and the guard decides to play a game. If you win, you will be allowed to leave. But if you lose, you die. The guard says that he is thinking of number 1, number 2, or number 3. You are allowed to ask one question to find out which of these three numbers the guard has in mind. However, the guard will only answer with a “yes”, “no”, or “I don’t know”. What should you say to the guard?
As ever, please feel free to say if you think you have a solution and how long it took, but please do NOT post your answers. Solution on Monday. Have a good weekend!
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May 21, 2010 at 6:05 am |
What did we do to you that you keep wanting to kill us?
May 21, 2010 at 6:20 am
Richard’s not a psychologist but a psychopath. The beginning is the same, but the end is very different!
May 21, 2010 at 6:41 am
lol …. how very true!
I’ve thought of several things….one being “please, please, please don’t kill me!”… lol… I’m sure that isn’t the answer.
May 21, 2010 at 6:30 am |
About five minutes this time.
May 21, 2010 at 6:41 am |
I think the fact that guard seems to have a “God” complex by so nonchalantly wielding the power of life and death, and therefore his answer to my question is likely to be untrue (what am I thinking, no wrong, death it is then….). I’ll lead the other prisoners in open revolt and play better odds of survival, thankyou
May 21, 2010 at 7:06 am |
I think I have an answer. I’m not too happy with it though because it seems to make an assumption about the level of education that a prison guard has.
May 21, 2010 at 7:08 am |
A couple of minutes to think of 2 “answers”, neither of which feel likely to be the ‘right’ ones -one maths based and one logic based.
May 21, 2010 at 7:15 am |
Mmm well I have an answer but is it the right one?
May 21, 2010 at 7:24 am |
I have one, but I doubt it’s the right question.
May 21, 2010 at 7:30 am |
I did this while driving to work, so road traffic distracted me, but I managed to get an answer in ten minutes. I think there’s clearly infinite different answers to this, but the idea is presumably to determine the required general strategy, which I think I have.
I agree there is a small assumption here that the guard is numerate and doesn’t lie
May 21, 2010 at 7:53 am |
Oooh i dont like this one!
May 21, 2010 at 8:55 am
hey Faye I wonder what the guard looks like is he good looking….hehe… and if my answer is wrong do I get one final request? {I don’t smoke either…lol…}
May 21, 2010 at 11:07 am
lol lila!
May 22, 2010 at 12:57 am
Whhaaattt?…. giggle …. wouldn’t want to waste my last request…lol….. :}
May 21, 2010 at 8:29 am |
I knew this one already, btw u assume the guard answers truthfully to ur question.
May 21, 2010 at 8:35 am |
I got an answer within two minutes. I get the feeling it won’t be the one that’s posted.
May 21, 2010 at 8:43 am |
Easy. Though my solution is probably not official and slightly rude to prison guards.
May 21, 2010 at 8:45 am |
Hmm, got one that seems rather neat in about a minute… Will be interested to see what other ways there might be of doing it.
May 21, 2010 at 8:52 am |
Got it, but it only works on the condition that the guard anwer truthfully.
About two minutes…
May 21, 2010 at 8:58 am |
About one minute. Of course it depends on the guard’s honesty – but that’s part of the ground rules for this sort of game, isn’t it?
May 21, 2010 at 9:07 am |
Phew, that was tricky. Saw the shape the answer had to be straight away but took about 10 minutes to work it out.
May 21, 2010 at 9:11 am |
I got a solution in two minutes and later on two more variations based on the same idea.
May 21, 2010 at 9:36 am |
Can someone do me a favor and email me the answer? I’m buggin’ out over here.
mikerpiker@gmail.com
May 21, 2010 at 10:00 am |
Ask a silly question, get a silly answer. I got a silly answer before I finished reading the question.
May 21, 2010 at 11:11 am
ha ha
May 21, 2010 at 10:10 am |
I have one that works, but will almost certainly not be the official answer.
It requires the guard to be honest and also have a good knowledge in genetics.
May 21, 2010 at 10:37 am |
I have an answer, but I think it might well be wrong.
I assumed that the guard would be honest in his response and that I am not allowed anything as simple as:
“say ‘yes’ if you are thinking of 1, say ‘no’ if you are thinking of 2 and say ‘don’t know’ if you are thinking of 3″
May 21, 2010 at 1:07 pm
That’s not a question though.
May 21, 2010 at 1:26 pm
This was pretty much the cheesy answer I came up with too. Easy to rephrase that into a question. Feels like cheating.
May 21, 2010 at 11:09 am |
Hmmmmmm why should he say “I dont know”……..
Im still trying to find the answer….
May 21, 2010 at 11:10 am |
oooooo i got it!!!!!
i think!!!!! is it a trick question???
May 21, 2010 at 12:04 pm |
I think I have a solution. It took me about three minutes.
May 21, 2010 at 12:09 pm |
solution immediately.
May 21, 2010 at 12:14 pm |
“The guard says that he is thinking of number 1, number 2, or number 3. ”
I don’t get that formulation … so, is it ANY three numbers (in a sense of: he is thinking of numbers A,B, and C) or is he thinking of THE numbers 1,2, or 3?
confuses me!
May 21, 2010 at 12:42 pm
me too thats wat i was thinking
May 21, 2010 at 12:25 pm |
I’m still working on an answer, or rather a question (10 minutes so far) but am moved to comment on that photograph of the guard, which is simply marvellous.
May 22, 2010 at 1:13 am
Yeah but is that part of a trick? Cause based on one of our more recent surveys he may only be of use as eye candy…lol…..
May 21, 2010 at 1:01 pm |
I haven’t got an answer yet, but what’s with that guard picture? Is this prison porn? I think if I were gay I might just stay in the cell with him.
May 21, 2010 at 1:31 pm |
I have a math-ish question that took me about 5 minutes to come up with. Seems unlikely but I think it works…
May 21, 2010 at 1:31 pm |
I think your prison guard’s pants are held together with Velcro.
May 21, 2010 at 1:34 pm |
5 minutes of sustained headscratching to arrive at watertight answer. No cheating or Googling this time. Nice puzzle.
May 21, 2010 at 1:35 pm |
BTW how is the guard in bed? LOL
May 22, 2010 at 1:22 am
based on looks? I guess awful…..roflao….. ;}
May 21, 2010 at 1:55 pm |
I guess I would have to ask, “Is that a regulation hair cut? Because it looks a little shaggy to me.”
May 21, 2010 at 2:00 pm |
I’d like it on record that I’d be more than happy to be held prisoner by that guard
May 21, 2010 at 2:04 pm |
After thinking a while, I did come up with an answer that would probably work the way I want it to work, but it’s phrased in a fairly ugly way…
May 21, 2010 at 2:05 pm |
Got this in five minutes. Not sure it’s right but it seems to work when tested.
May 21, 2010 at 2:15 pm |
Can we assume that the guard must answer truthfully? It’s not explicitly stated, and I can’t think of a way to solve it if he’s allowed to lie.
May 21, 2010 at 2:16 pm |
Of the recent puzzles, this was the easiest for me – took me a minute or so with the initial hunch of what to ask a few seconds after reading. There are many variants to my solution.
May 21, 2010 at 2:36 pm |
Umm, that guard looks like a stripogram… but I have one question and it took me about 5 seconds to think of it.
May 21, 2010 at 3:02 pm |
Got an answer in about 2 minutes, prob not correct. We’ll see
May 21, 2010 at 3:35 pm |
Under a minute for the core idea. Crafting a question that actually implements the idea somewhat longer.
May 21, 2010 at 3:36 pm |
I think there are several ways of doing this, although, maybe not very elegant any of them.
Nice puzzle…
May 21, 2010 at 3:37 pm |
I have an answer (or question rather) and unlike a lot of other people posting I feel pretty confident about it…..*smugness*
May 21, 2010 at 3:37 pm |
This is a bad puzzle (only the second bad one that I can recall). There is a direct mapping of 3 number/answer pairs, so the only thing to do is make up a suitable question. The computer scientist in me got *a* solution immediately, but there are an infinite number of questions that would serve as solutions. Maybe a better puzzle would be how *short* a question can you think of that saves your life?
May 21, 2010 at 4:00 pm |
I’ve got one, took about 2 minutes.
May 21, 2010 at 4:11 pm |
Got it! About two minutes. I’m getting better at these.
May 21, 2010 at 4:35 pm |
I have an answer that I believe provides the solution. Took about a minute. Of course, it’s maths/logic related because that’s my area of training.
May 21, 2010 at 5:06 pm |
Can someone please give me a hint? I’m having some brain fog today.
May 21, 2010 at 5:09 pm |
I don’t recall a prison guard amongst the cast of the Village People, but that was a long time ago…
May 21, 2010 at 5:26 pm |
It’s a silly question. Everyone knows the three choices are “Yes”, “No”, and “FileNotFound”:
http://thedailywtf.com/Articles/What_Is_Truth_0x3f_.aspx
May 21, 2010 at 5:38 pm |
By Jove, I think I’ve got it! In just a couple of minutes or so. I’ve got to start timing myself. I’m usually pretty horrid with games like these but I’ve answered a couple pretty easily.
May 21, 2010 at 8:41 pm |
Got it in about 10 minutes.
The breakthrough was realising I needed to utilise all three possible responses.
May 22, 2010 at 12:09 am |
[...] It’s the Friday Puzzle! You are trapped in a prison and the guard decides to play a game. If you win, you will be allowed to leave. But if [...] [...]
May 22, 2010 at 4:41 am |
I have an idea of what a good question might be, but if the guard’s mathematically challenged, it might be hard…
I’d probably have to phrase it carefully so that even the guard would understand. It’s a given that he can’t lie, right?
May 22, 2010 at 5:46 am |
4-5 minutes to one solution. This is harder than the others. Thanks for it!
May 22, 2010 at 12:15 pm |
goog one Richypitchy. kept me busy for a few minutes!
May 22, 2010 at 3:58 pm |
I got an answer in about 5 minutes.
May 22, 2010 at 6:27 pm |
Had a little think, is the answer perhaps:
‘Is the number you’re thinking of less than 2?’
A ‘yes’ answer would mean it had to be 1, ‘no’ would mean 3, ‘don’t know’ would be 2 perhaps? Just a guess!!
Emma x
May 23, 2010 at 2:54 pm
You didn’t read well!
May 23, 2010 at 2:57 pm
you mist the last paragraph I will copy it for you.
…As ever, please feel free to say if you think you have a solution and how long it took, but please do NOT post your answers….
May 22, 2010 at 6:28 pm |
In fact, no that wouldn’t work! Scrap that last post lol!
May 22, 2010 at 11:19 pm |
Guess what? Some of us have created a TEAM ANSWER. We laughed, we cried, we got distracted by cartoons and butterflies – but in the end, we did it. If it’s not right, our new friendship will be shattered and we will be broken individuals.
May 22, 2010 at 11:28 pm
Okay, my buddies want you to know that the butteflies are all in my bedroom (in pupae form) so did not distract them, just me, and the cartoons were inside my head, and so it was just me distracted by those too.
May 22, 2010 at 11:30 pm
We were distracted by ScreamingGreenConure’s distraction.
May 22, 2010 at 11:32 pm
She distracted us from distracting her. Be glad, we still wouldn’t have solved it if she hadn’t. Thank you, butterfly pupae. We owe you our freedom.
May 22, 2010 at 11:33 pm
I’m very distracting. Look, I’m distracting you right now!
May 23, 2010 at 1:52 am
Well SGC lives…I was wondering if you got lost in the future trying to find the answer…lol…with all the distracting going on did anyone get distracted by the guard? Remember your life is in his hands….lol….hmmm….now that’s a thought…… ;}
May 23, 2010 at 3:46 am |
Hm. . That was easy i guess. . Less than 1 min. . . . But my answer may be wrong. . Let’s see
May 23, 2010 at 6:03 am |
Hah, after a few minutes wondering if the problem *might* be related to the famous “Monty Hall” problem, I abandoned that path and asked the guard a tricky question…
(I assume that the goal to seek is to not get killed?)
May 23, 2010 at 7:38 am |
Oh wow, I have run through everything I can think of and none of them are passing the test. I don’t know. Infuriating!
May 23, 2010 at 12:40 pm |
I think my question is “Does the ‘Prisoners’ Last Meal’ menu have a veggie option please?”
May 23, 2010 at 2:24 pm
Guard: “meeeeh, I don’t know”
May 23, 2010 at 3:24 pm |
The guard is actually thinking?! Well, that’s something new.
I might have an answer, but it probably isn’t the right one.
May 23, 2010 at 9:50 pm |
10 seconds. Still a good puzzle
May 23, 2010 at 10:00 pm |
If you added the number you are thinking of to three, what would it equal?
May 23, 2010 at 10:01 pm |
Whoops, sorry, how do I delete my post? I didn’t notice the “don’t post your answer here” at the top. My bad!
May 23, 2010 at 10:14 pm |
The question would be,
Is the difference between your number and the number 1 an even number?
If he said yes, then the number is 3 (3-1=2) even
If he said no, then the number is 2 (2-1=1) odd
If he said I dunno, then the number is 1(1-1=0) neither even or odd (dunno)
This answer can’t be proved wrong
I hope 
May 23, 2010 at 11:19 pm |
zero is even.
May 24, 2010 at 4:50 am
Oh yea!! But may be the guard is bad in math, and he would say “I dunno” :p
btw, where should I post my answers, if not here?
May 24, 2010 at 6:10 pm |
“When you divide the number you’re thinking of by that number -1 (x/x-1), is the answer greater than 1.75?”
3 – If the number is 3, the expression is 3/ (3-1) = 3/2 = 1.5 – answer ‘No’ (NOT greater than 1.75)
2 – If the number is 2, the expression is 2/(2-1) = 2/1 = 2 – answer “Yes” (greater than 1.75)
1 – If the number is 1, the expression is 1/(1-1) = 1/0 = undefined – answer “I don’t know”
May 24, 2010 at 8:55 pm |
How about this:
“If I guess incorrectly, would your number be larger than mine?”
If “yes” then hypothetical guess {1,2} => 3
If “I don’t know” then hypothetical guess {1,3} => 2
If “no” then hypothetical guess {2,3} => 1
May 24, 2010 at 8:57 pm
Oops, I meant to answer on the correct page!
June 19, 2010 at 4:53 pm |
Want to subscribe for Frday puzzle.
October 20, 2011 at 9:43 pm |
foo bar