When Is Cheryl’s Birthday?
April 14, 2015 10:32 AM Subscribe
It's a good problem. And it's logic rather than math, which western news articles continue to mischaracterize it as.
I confess I got it wrong on my first attempt. I was mostly right, but I didn't follow through the implications of Albert's final statement.
posted by figurant at 10:39 AM on April 14, 2015 [3 favorites]
I confess I got it wrong on my first attempt. I was mostly right, but I didn't follow through the implications of Albert's final statement.
posted by figurant at 10:39 AM on April 14, 2015 [3 favorites]
Pretty sure Cherly's birthday is blue and gold.
posted by gwint at 10:41 AM on April 14, 2015 [7 favorites]
posted by gwint at 10:41 AM on April 14, 2015 [7 favorites]
It's not a hard question, but it requires the sort of lateral thinking you only find in a Sierra adventure game.
posted by NoxAeternum at 10:44 AM on April 14, 2015 [7 favorites]
posted by NoxAeternum at 10:44 AM on April 14, 2015 [7 favorites]
It's a test of whether or not you've been exposed to logic puzzles before. I actually haven't seen this particular one, but "several people have partial information" is a pretty common form. For some reason, I've most often seen this puzzle in the form of people trying to guess the color of their own hat.
posted by muddgirl at 10:45 AM on April 14, 2015 [12 favorites]
posted by muddgirl at 10:45 AM on April 14, 2015 [12 favorites]
then got sad that I felt smart for solving a dumb puzzle that a bunch of middle schoolers had to solve.
From the article: It turned out the problem actually came from a math olympiad test for math-savvy high school-age students.
Though honestly it does feel a little bit too straightforward for high school and up olympiad questions.
posted by kmz at 10:45 AM on April 14, 2015
From the article: It turned out the problem actually came from a math olympiad test for math-savvy high school-age students.
Though honestly it does feel a little bit too straightforward for high school and up olympiad questions.
posted by kmz at 10:45 AM on April 14, 2015
So I am smart!
posted by (Arsenio) Hall and (Warren) Oates at 10:50 AM on April 14, 2015
posted by (Arsenio) Hall and (Warren) Oates at 10:50 AM on April 14, 2015
Ah, MetaFilter. The place where I come to be reminded that I suck at logic problems that 12 year olds can solve, to the extent that the answers have me weeping in bewilderment. Right before people come in to explain exactly why they're really easy. If anyone needs me I'll be over in the corner resting in the fetal position.
posted by billiebee at 11:00 AM on April 14, 2015 [8 favorites]
posted by billiebee at 11:00 AM on April 14, 2015 [8 favorites]
ps cheryl is a dick
posted by billiebee at 11:00 AM on April 14, 2015 [28 favorites]
posted by billiebee at 11:00 AM on April 14, 2015 [28 favorites]
SPOILER ALERT FOR THE ARTICLE
Cheryl is a Cancer, which still does not explain her behavior.
I loved this phrase. Like, the REAL puzzle is "WTF is up with Cheryl? Who ACTS like that?" and we use the only information we have -- her date of birth -- to try to solve this but, even knowing she is a Cancer, we still can't work our way through it. I have done tons of logic puzzles and this sentence's combination of astrology, logic, and straightforwardness delights me.
posted by Mrs. Pterodactyl at 11:01 AM on April 14, 2015 [14 favorites]
Cheryl is a Cancer, which still does not explain her behavior.
I loved this phrase. Like, the REAL puzzle is "WTF is up with Cheryl? Who ACTS like that?" and we use the only information we have -- her date of birth -- to try to solve this but, even knowing she is a Cancer, we still can't work our way through it. I have done tons of logic puzzles and this sentence's combination of astrology, logic, and straightforwardness delights me.
posted by Mrs. Pterodactyl at 11:01 AM on April 14, 2015 [14 favorites]
(Arsenio) Hall and (Warren) Oates -- yeah, but how many kindergarteners can you take on at once ?
posted by k5.user at 11:01 AM on April 14, 2015 [1 favorite]
posted by k5.user at 11:01 AM on April 14, 2015 [1 favorite]
I got it. Neat question, especially because it does not require any actual math, just some logic and maybe crossing out boxes. I was stymied until I actually thought about the last statement.
posted by Hactar at 11:01 AM on April 14, 2015
posted by Hactar at 11:01 AM on April 14, 2015
Yes! I got it, and I suck at math. But I'm great at logic. Sucks to your assmar, middle-schoolers!!
posted by taz at 11:06 AM on April 14, 2015 [3 favorites]
posted by taz at 11:06 AM on April 14, 2015 [3 favorites]
The problem does not state that Albert and Bernard are incapable of error and always speak the truth. Without those assumptions, the problem cannot be solved.
posted by ubiquity at 11:09 AM on April 14, 2015 [5 favorites]
posted by ubiquity at 11:09 AM on April 14, 2015 [5 favorites]
Right before people come in to explain exactly why they're really easy. If anyone needs me I'll be over in the corner resting in the fetal position.
It should be easy for anyone who has an interest in and exposure to logic problems. Like I said, it's a pretty classic form. But I wouldn't expect it to be easy for someone who hasn't learned how to solve it!
High schoolers who do math olympiad should be much better at solving this problem than the average adult. That's not an insult. It has nothing to do with being stupid or smart.
posted by muddgirl at 11:10 AM on April 14, 2015 [4 favorites]
It should be easy for anyone who has an interest in and exposure to logic problems. Like I said, it's a pretty classic form. But I wouldn't expect it to be easy for someone who hasn't learned how to solve it!
High schoolers who do math olympiad should be much better at solving this problem than the average adult. That's not an insult. It has nothing to do with being stupid or smart.
posted by muddgirl at 11:10 AM on April 14, 2015 [4 favorites]
Anyone who's read Raymond Smullyan should be able to get this one easily. I've seen a similar problem, but it's about numbers, where one knows the sum and the other knows the product.
posted by salmacis at 11:12 AM on April 14, 2015 [2 favorites]
posted by salmacis at 11:12 AM on April 14, 2015 [2 favorites]
Without those assumptions, the problem cannot be solved.
Our high school chem exams had diagrams of equipment, the instructions asking you to describe how you'd perform a given experiment or produce a product with the equipment pictured.
Answering, "there are no goggles; the experiment cannot be done" didn't get you any points there, either.
posted by uncleozzy at 11:12 AM on April 14, 2015 [15 favorites]
Our high school chem exams had diagrams of equipment, the instructions asking you to describe how you'd perform a given experiment or produce a product with the equipment pictured.
Answering, "there are no goggles; the experiment cannot be done" didn't get you any points there, either.
posted by uncleozzy at 11:12 AM on April 14, 2015 [15 favorites]
Okay, confused. Spoilers, obviously.
Taking Albert's first statement 'I don't know, and I know that Bernard doesn't know either', you can eliminate May and June, because if Cheryl had said '18' or '19' to B, then he would know automatically the date as those numbers are unique.
B now knows this. Suppose, then, that C had said '17'. There is only one '17' left - August 17th. He could then, quite logically say that he now knew the date.
A could not say 'I now know' because logically it could be any one of '15', '16' or '17'. He doesn't know how B came to know the answer, which would make A unreliable, but it wouldn't make B's response invalid.
Why is this answer wrong, other than the unspoken rule that there is a unique answer?
posted by YAMWAK at 11:12 AM on April 14, 2015 [1 favorite]
Taking Albert's first statement 'I don't know, and I know that Bernard doesn't know either', you can eliminate May and June, because if Cheryl had said '18' or '19' to B, then he would know automatically the date as those numbers are unique.
B now knows this. Suppose, then, that C had said '17'. There is only one '17' left - August 17th. He could then, quite logically say that he now knew the date.
A could not say 'I now know' because logically it could be any one of '15', '16' or '17'. He doesn't know how B came to know the answer, which would make A unreliable, but it wouldn't make B's response invalid.
Why is this answer wrong, other than the unspoken rule that there is a unique answer?
posted by YAMWAK at 11:12 AM on April 14, 2015 [1 favorite]
A knows the month. If the month he knew had been August, he would not have been able to solve the problem. But because he was able to solve the problem (and because we assume he is incapable of error, and always speaks the truth), we can conclude the month he knew was July.
posted by ubiquity at 11:18 AM on April 14, 2015 [2 favorites]
posted by ubiquity at 11:18 AM on April 14, 2015 [2 favorites]
It's the third statement. Because if B knows based on A's first statement, A can now confirm that it is July.
posted by Rock Steady at 11:20 AM on April 14, 2015
posted by Rock Steady at 11:20 AM on April 14, 2015
It's a test of whether or not you've been exposed to logic puzzles before.
Yes, this. The problem it hard if you haven't done these kinds of puzzles before. Integration by u-substitution would also be incredibly hard if no one had explained to you how to do that kind of problem. Yet millions of US high school students compute those integrals, no problem, because it's what's on the curriculum.
posted by escabeche at 11:23 AM on April 14, 2015 [3 favorites]
Yes, this. The problem it hard if you haven't done these kinds of puzzles before. Integration by u-substitution would also be incredibly hard if no one had explained to you how to do that kind of problem. Yet millions of US high school students compute those integrals, no problem, because it's what's on the curriculum.
posted by escabeche at 11:23 AM on April 14, 2015 [3 favorites]
He doesn't know how B came to know the answer
Albert does know that the month is July, so it's either July 14th or July 16th. Albert knows that Cheryl couldn't have told Bernard that the date was the 17th, because we have to assume that Cheryl is being honest, otherwise it's not a logic puzzle.
posted by muddgirl at 11:24 AM on April 14, 2015
Albert does know that the month is July, so it's either July 14th or July 16th. Albert knows that Cheryl couldn't have told Bernard that the date was the 17th, because we have to assume that Cheryl is being honest, otherwise it's not a logic puzzle.
posted by muddgirl at 11:24 AM on April 14, 2015
Good one Cheryl! You got us there.
Hey, would you mind feeding my cat? He's down in the crawlspace...
posted by Naberius at 11:28 AM on April 14, 2015 [4 favorites]
Hey, would you mind feeding my cat? He's down in the crawlspace...
posted by Naberius at 11:28 AM on April 14, 2015 [4 favorites]
And now I see that this is not primary school homework, as originally publicized, but actually a high school olympiad problem. In which case, what kmz said -- it's kind of too easy for a test of that kind!
posted by escabeche at 11:31 AM on April 14, 2015 [1 favorite]
posted by escabeche at 11:31 AM on April 14, 2015 [1 favorite]
Also, re:
And it's logic rather than math, which western news articles continue to mischaracterize it as
and
it does not require any actual math, just some logic
Dude! Just because formal logic doesn't involve numbers doesn't mean it's not math.
posted by escabeche at 11:34 AM on April 14, 2015 [6 favorites]
And it's logic rather than math, which western news articles continue to mischaracterize it as
and
it does not require any actual math, just some logic
Dude! Just because formal logic doesn't involve numbers doesn't mean it's not math.
posted by escabeche at 11:34 AM on April 14, 2015 [6 favorites]
I'll give you a simpler one, from a Japanese entrance exam for kindergarten.
Which box is heaviest?
You must answer within 60 seconds or receive a failing score.
posted by charlie don't surf at 11:35 AM on April 14, 2015 [1 favorite]
Which box is heaviest?
You must answer within 60 seconds or receive a failing score.
posted by charlie don't surf at 11:35 AM on April 14, 2015 [1 favorite]
IIRC, logic puzzles were part & parcel of my high school math curriculum.
posted by grumpybear69 at 11:35 AM on April 14, 2015
posted by grumpybear69 at 11:35 AM on April 14, 2015
Is this the Cheryl in question? Because that would explain a lot.
posted by The Nutmeg of Consolation at 11:38 AM on April 14, 2015 [4 favorites]
posted by The Nutmeg of Consolation at 11:38 AM on April 14, 2015 [4 favorites]
Common Core is really getting out of hand.
posted by Renoroc at 11:41 AM on April 14, 2015 [2 favorites]
posted by Renoroc at 11:41 AM on April 14, 2015 [2 favorites]
Which box is heaviest?
Um, unless that's not actually a circle in diagram 2, I don't think this works.
1. Circle = 2 X
2. Circle also = 2 Diamond (so X and Diamond should be the same.)
3. Triangle is heavier than Circle, which weighs the same as 2 Diamonds.
Yet,
4. 1 Diamond is heavier than 1 Triangle - but we've previously established that 1 Triangle is heavier than 1 Circle, which is twice as heavy as a Diamond.
Or am I missing the point entirely?
posted by Naberius at 11:41 AM on April 14, 2015 [2 favorites]
Um, unless that's not actually a circle in diagram 2, I don't think this works.
1. Circle = 2 X
2. Circle also = 2 Diamond (so X and Diamond should be the same.)
3. Triangle is heavier than Circle, which weighs the same as 2 Diamonds.
Yet,
4. 1 Diamond is heavier than 1 Triangle - but we've previously established that 1 Triangle is heavier than 1 Circle, which is twice as heavy as a Diamond.
Or am I missing the point entirely?
posted by Naberius at 11:41 AM on April 14, 2015 [2 favorites]
it's kind of too easy for a test of that kind!
I read somewhere else (think it was a Metro paper last week) that the question was actually considered pretty tough, to weed out the very brightest young logicians. Who I assume are now locked away working in whatever Singapore's equivalent of Bletchley Park is.
posted by Flashman at 11:42 AM on April 14, 2015 [1 favorite]
I read somewhere else (think it was a Metro paper last week) that the question was actually considered pretty tough, to weed out the very brightest young logicians. Who I assume are now locked away working in whatever Singapore's equivalent of Bletchley Park is.
posted by Flashman at 11:42 AM on April 14, 2015 [1 favorite]
There are two circles - white circle and black circle with dot.
White circle is heavier than X. (1)
Triangle is heavier than white circle. (3)
Diamond is heavier than triangle. (4)
Black circle with dot is heavier than diamond. (2)
Therefore black circle with dot is heaviest.
posted by grumpybear69 at 11:50 AM on April 14, 2015 [4 favorites]
White circle is heavier than X. (1)
Triangle is heavier than white circle. (3)
Diamond is heavier than triangle. (4)
Black circle with dot is heavier than diamond. (2)
Therefore black circle with dot is heaviest.
posted by grumpybear69 at 11:50 AM on April 14, 2015 [4 favorites]
The problem does not state that Albert and Bernard are incapable of error and always speak the truth. Without those assumptions, the problem cannot be solved.Well, if they are perfectly logical, they don't speak the truth about their own ability to understand the implications of their statements on their partner. Why doesn't the ever-logical Bernard completely tell the truth, and state "I didn’t know originally, but now I do. And now that I have said this out loud, I can deduce that Albert will deduce the correct date."
And why doesn't Albert say, to start with, "I don’t know when your birthday is, but I know Bernard doesn’t know, either. However, there is a case in which if Bernard hears me say what I just said, he will deduce the correct date, and there is a further case where I will be able to deduce the correct date if I hear him say that."
Also, The Hardest Logic Puzzle Ever.
posted by sylvanshine at 12:00 PM on April 14, 2015 [2 favorites]
Or am I missing the point entirely?
No, that is exactly the point of this question. It was designed that way to confuse 5 year old kids. A smart kid would know how to verify the circles were different symbols.
posted by charlie don't surf at 12:04 PM on April 14, 2015
No, that is exactly the point of this question. It was designed that way to confuse 5 year old kids. A smart kid would know how to verify the circles were different symbols.
posted by charlie don't surf at 12:04 PM on April 14, 2015
I just barely got the dark circle in within 60 seconds. Whew.
posted by roomthreeseventeen at 12:04 PM on April 14, 2015
posted by roomthreeseventeen at 12:04 PM on April 14, 2015
Oh you guys like logic puzzles? If you live in a major city, go check out Puzzled Pint. It's tonight! (And every month.)
posted by phunniemee at 12:08 PM on April 14, 2015 [1 favorite]
posted by phunniemee at 12:08 PM on April 14, 2015 [1 favorite]
This just makes me miss Tom Magliozzi.
posted by peeedro at 12:16 PM on April 14, 2015 [4 favorites]
posted by peeedro at 12:16 PM on April 14, 2015 [4 favorites]
I feel like an idiot reading through these comments. Not only could I not arrive at the right answer on my own, but I also cannot understand the explanation of the problem. All I know is that Cheryl is a terrible person.
posted by Annabelle74 at 12:16 PM on April 14, 2015 [4 favorites]
posted by Annabelle74 at 12:16 PM on April 14, 2015 [4 favorites]
I am at the same point as you are, Annabell74. Cheryl is absolutely a shit.
posted by Sternmeyer at 12:18 PM on April 14, 2015 [3 favorites]
posted by Sternmeyer at 12:18 PM on April 14, 2015 [3 favorites]
Also, The Hardest Logic Puzzle Ever.
SPOILERS AHEAD FOR HARDEST LOGIC PUZZLE EVER:
sylvanshine, I got Cheryl's birthday correctly, following the same logic given in the solution, but I'm having trouble with the green-eyed dragons. Can you or anyone else resolve this for me?
"Do I have green eyes? I don't know. But if I do not, then this other dragon, upon seeing my non-green eyes, will know instantly and unambiguously that he is the one with green eyes, and at midnight will turn into a sparrow."
This makes sense, because of the implication that the speaker reasons correctly that he does not know whether the other dragon is aware of the presence of any green-eyed dragons. But here's where the solution breaks down for me:
Let's expand the problem to 3 green-eyed dragons. Following your announcement, each dragon thinks to itself that if it does not have green eyes, then the other two dragons will determine their eye color by the reasoning laid out in the 2 green-eyed dragon scenario presented above.
With three or more dragons, each dragon knows that there is at least one green-eyed dragon, but he or she also knows that each other dragon also knows that there is at least one green-eyed dragon, which leaves open the possiblity of one non-green-eyed dragon. What am I missing?
posted by ogooglebar at 12:42 PM on April 14, 2015
SPOILERS AHEAD FOR HARDEST LOGIC PUZZLE EVER:
sylvanshine, I got Cheryl's birthday correctly, following the same logic given in the solution, but I'm having trouble with the green-eyed dragons. Can you or anyone else resolve this for me?
"Do I have green eyes? I don't know. But if I do not, then this other dragon, upon seeing my non-green eyes, will know instantly and unambiguously that he is the one with green eyes, and at midnight will turn into a sparrow."
This makes sense, because of the implication that the speaker reasons correctly that he does not know whether the other dragon is aware of the presence of any green-eyed dragons. But here's where the solution breaks down for me:
Let's expand the problem to 3 green-eyed dragons. Following your announcement, each dragon thinks to itself that if it does not have green eyes, then the other two dragons will determine their eye color by the reasoning laid out in the 2 green-eyed dragon scenario presented above.
With three or more dragons, each dragon knows that there is at least one green-eyed dragon, but he or she also knows that each other dragon also knows that there is at least one green-eyed dragon, which leaves open the possiblity of one non-green-eyed dragon. What am I missing?
posted by ogooglebar at 12:42 PM on April 14, 2015
So historically speaking I suck at this kind of stuff but I got it right on the first try so now I am parading around my apartment like I am The Boss and my cat is giving me the most withering looks from the corner she retreated to after my celebratory outburst scared the crap out of her.
posted by Hermione Granger at 12:42 PM on April 14, 2015 [5 favorites]
posted by Hermione Granger at 12:42 PM on April 14, 2015 [5 favorites]
ogooglebar: A similar puzzle (with more or less identical reasoning) to the green-eyed dragon puzzle was discussed at great length on MetaFilter in 2008.
P.S. I got the "World's (Other) Hardest Logic Puzzle" (the three gods) in about half an hour. But I've seen a lot of Smullyan-type puzzles before, which laid a lot of the groundwork.
posted by DevilsAdvocate at 12:55 PM on April 14, 2015 [1 favorite]
P.S. I got the "World's (Other) Hardest Logic Puzzle" (the three gods) in about half an hour. But I've seen a lot of Smullyan-type puzzles before, which laid a lot of the groundwork.
posted by DevilsAdvocate at 12:55 PM on April 14, 2015 [1 favorite]
It's 66% not 50% because he knows what is behind the doors.
posted by Pogo_Fuzzybutt at 1:04 PM on April 14, 2015 [1 favorite]
posted by Pogo_Fuzzybutt at 1:04 PM on April 14, 2015 [1 favorite]
June 17 because that's my wife's birthday and she would kill me for forgetting.
posted by dances_with_sneetches at 1:17 PM on April 14, 2015
posted by dances_with_sneetches at 1:17 PM on April 14, 2015
ogooglebar, consider the point of view of dragon 3. Dragon 3 can see two dragons with green eyes. Dragons 1 and 2 can either see two green-eyed dragons (if dragon 3 has green eyes), or else one dragon with green eyes (if dragon 3 has brown eyes, say).
If dragons 1 and 2 can only see one green eyed dragon, and that dragon doesn't disappear, then dragons 1 and 2 would immediately realise that they too must have green eyes. Thus both dragons would disappear. If, however, both dragons could see two other dragons with green eyes, they wouldn't disappear.
As dragon 3 sees that 1 and 2 don't disappear, dragon 3 realises that they too has green eyes.
posted by YAMWAK at 1:23 PM on April 14, 2015 [1 favorite]
If dragons 1 and 2 can only see one green eyed dragon, and that dragon doesn't disappear, then dragons 1 and 2 would immediately realise that they too must have green eyes. Thus both dragons would disappear. If, however, both dragons could see two other dragons with green eyes, they wouldn't disappear.
As dragon 3 sees that 1 and 2 don't disappear, dragon 3 realises that they too has green eyes.
posted by YAMWAK at 1:23 PM on April 14, 2015 [1 favorite]
Thanks, I got it. That common knowledge concept is one I hadn't encountered before, and it took a bit to wrap my mind around it. I'm not certain that I could coherently explain it to someone else yet, though.
posted by ogooglebar at 1:27 PM on April 14, 2015
posted by ogooglebar at 1:27 PM on April 14, 2015
BTW if anyone is interested where that kindergarten exam question came from, I just repaired the source on my website. In 2002, I posted Take The Kindergarten Entrance Exam which includes a 15 minute video in Japanese (with no English subtitles but my commentary). It describes the rigorous mental and physical preparation for the Kindergarten entrance exam.
posted by charlie don't surf at 1:31 PM on April 14, 2015
posted by charlie don't surf at 1:31 PM on April 14, 2015
Argh, I feel like an idiot for not getting this. I understand why it can't be the 18th or 19th, and I understand the last 2 steps and why it has to be July 16th. What I don't understand is why May was eliminated as a choice in step 1, and Albert knows that Bernard must have been told July or August? There are still 2 dates with dual options left in May? Halp
posted by widdershins at 2:22 PM on April 14, 2015
posted by widdershins at 2:22 PM on April 14, 2015
What I don't understand is why May was eliminated as a choice in step 1,
May and June are eliminated because no other months have 18 or 19 as possibilities. If Bernard was told 19, he would know the answer was May 19th. Albert is sure Bernard doesn't know the answer, so Albert can't have been told 'May.' If Albert had been told May, it would be possible for Bernard to be sure of the answer.
posted by BungaDunga at 2:42 PM on April 14, 2015 [1 favorite]
May and June are eliminated because no other months have 18 or 19 as possibilities. If Bernard was told 19, he would know the answer was May 19th. Albert is sure Bernard doesn't know the answer, so Albert can't have been told 'May.' If Albert had been told May, it would be possible for Bernard to be sure of the answer.
posted by BungaDunga at 2:42 PM on April 14, 2015 [1 favorite]
Albert and Bernard just became friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 10 possible dates. Albert and Bernard aren't interested in her shit and quickly defriend her, and Cheryl learns what it is to be alone in the world forever.
posted by turbid dahlia at 2:45 PM on April 14, 2015 [8 favorites]
posted by turbid dahlia at 2:45 PM on April 14, 2015 [8 favorites]
If Bernard was told that the date was the 18th or the 19th, then he would know the birthday right away - if he was told 18, then the birthday has to be June 18. If he was told 19, then the birthday has to be May 19.
But Albert knows that Bernard wasn't told either of those numbers. He knows that Bernard was told either the 14th or the 16th. That's why he says "I don't know the birthday, but I do know that Bernard doesn't know it, either." That's how we eliminate May and June. It doesn't have to do with what Bernard knows, but with what Albert knows. If it was in May or June, Albert couldn't confidently state that Bernard didn't know the birthday.
posted by muddgirl at 2:47 PM on April 14, 2015 [1 favorite]
But Albert knows that Bernard wasn't told either of those numbers. He knows that Bernard was told either the 14th or the 16th. That's why he says "I don't know the birthday, but I do know that Bernard doesn't know it, either." That's how we eliminate May and June. It doesn't have to do with what Bernard knows, but with what Albert knows. If it was in May or June, Albert couldn't confidently state that Bernard didn't know the birthday.
posted by muddgirl at 2:47 PM on April 14, 2015 [1 favorite]
*opens door, gets a goat*
posted by dr_dank at 3:09 PM on April 14, 2015 [2 favorites]
posted by dr_dank at 3:09 PM on April 14, 2015 [2 favorites]
A smart kid would know how to verify the circles were different symbols.
Oh... So, um, what are you implying there?
posted by Naberius at 3:35 PM on April 14, 2015
Oh... So, um, what are you implying there?
posted by Naberius at 3:35 PM on April 14, 2015
A Problem of Logic
posted by (Arsenio) Hall and (Warren) Oates at 4:02 PM on April 14, 2015 [1 favorite]
posted by (Arsenio) Hall and (Warren) Oates at 4:02 PM on April 14, 2015 [1 favorite]
Thank you, muddgirl. After reading your explanation, light finally dawned. Now, at long last, I see how to solve the problem.
I would have probably gone to my grave not understanding it, though, if I'd been left to solve it entirely on my own.
posted by Annabelle74 at 4:20 PM on April 14, 2015 [1 favorite]
I would have probably gone to my grave not understanding it, though, if I'd been left to solve it entirely on my own.
posted by Annabelle74 at 4:20 PM on April 14, 2015 [1 favorite]
This was about to give me an aneurysm before I realized that I had mixed up Albert and Bernard.
posted by Bugbread at 4:31 PM on April 14, 2015 [1 favorite]
posted by Bugbread at 4:31 PM on April 14, 2015 [1 favorite]
I'm confused about the Gods puzzle.
Let's say I know I'm speaking to the truthful god, and asking about the random one.
I ask "If I asked the random guy if he is a parrot, what would he say?"
How would the truthful god answer? I mean, he doesn't *know* what the random guy would say. Am I just not allowed to ask such questions?
posted by nat at 4:44 PM on April 14, 2015
Let's say I know I'm speaking to the truthful god, and asking about the random one.
I ask "If I asked the random guy if he is a parrot, what would he say?"
How would the truthful god answer? I mean, he doesn't *know* what the random guy would say. Am I just not allowed to ask such questions?
posted by nat at 4:44 PM on April 14, 2015
I had the same question, nat, so I skipped to the answer. It turns out that there are two points of view: (1) you're not allowed that question, or there's some other restriction that makes the truthteller or the lieteller give a random answer, or (2) it makes their head explode, in which case the problem is slightly easier so in that case you only get two questions.
posted by muddgirl at 4:49 PM on April 14, 2015
posted by muddgirl at 4:49 PM on April 14, 2015
Thanks BungaDunga, that helped! I love logic puzzles, too, so was really frustrated I couldn't get it.
posted by widdershins at 5:03 PM on April 14, 2015
posted by widdershins at 5:03 PM on April 14, 2015
How would the truthful god answer? I mean, he doesn't *know* what the random guy would say.
The published answer touches on that a bit without reaching a conclusion one way or the other, but it's possible to find a solution that doesn't depend on whether the truthful or lying gods can predict future answers of the random god.
posted by DevilsAdvocate at 6:17 PM on April 14, 2015
The published answer touches on that a bit without reaching a conclusion one way or the other, but it's possible to find a solution that doesn't depend on whether the truthful or lying gods can predict future answers of the random god.
posted by DevilsAdvocate at 6:17 PM on April 14, 2015
It's probably been linked here before, but: How to tell you are in a logic puzzle.
- It is customary in your town to greet a new acquaintance by guessing the ages of his or her siblings.
- You are a compulsive liar. You can’t help it; everyone in your family is one too, as is everyone in your town, and indeed, your entire nation. You border a nation where everybody tells the truth.
- You are a compulsive liar, but this has not stopped you from making friends with someone who never lies. You met at your job, where you are both customer service representatives at the entrance to your local archaeological wonder/mystery spot. People are always asking one of you how the other feels about things. It’s ridiculous, you think, like, what are you asking me for?
Man that was easy. Person A says : it's a month without a unique day, July or August. Person B says "of July and August it's on a day they don't share, so it's not the 14th", and A says "Because I was told it's July, it must be July 16." If A had been told August he couldn't have got to the answer because there would be two candidate dates not one, so it's July.
posted by w0mbat at 8:26 PM on April 14, 2015 [2 favorites]
posted by w0mbat at 8:26 PM on April 14, 2015 [2 favorites]
so everyone's going on about Cheryl being a dick but what kind of jerks are Albert and Bernard that they can't just tell each other what they know and have done with it?
posted by 5_13_23_42_69_666 at 11:16 PM on April 14, 2015 [1 favorite]
posted by 5_13_23_42_69_666 at 11:16 PM on April 14, 2015 [1 favorite]
This reminds of a post from the excellent Thanks textbooks
My favourite weighs nine-tenths of its weight plus nine-tenths of a pound. What does it weigh?
This brings up several more important questions: Who has a “favorite” orange? How long have you had this orange that you’ve bonded with it so much? Who has an equation to calculate the weight of an orange?Is it your favorite because it happens to weigh nine pounds!?
posted by BigCalm at 1:46 AM on April 15, 2015 [2 favorites]
My favourite weighs nine-tenths of its weight plus nine-tenths of a pound. What does it weigh?
This brings up several more important questions: Who has a “favorite” orange? How long have you had this orange that you’ve bonded with it so much? Who has an equation to calculate the weight of an orange?Is it your favorite because it happens to weigh nine pounds!?
posted by BigCalm at 1:46 AM on April 15, 2015 [2 favorites]
I'm having (possibly spurious) issues with how/in what sense A initially knows that B doesn't know, and it appears I'm not alone.
posted by progosk at 6:34 AM on April 15, 2015 [1 favorite]
posted by progosk at 6:34 AM on April 15, 2015 [1 favorite]
I think that's why Kenneth Chang rewrote the question slightly, to make explicit the assumption that Albert makes his first statement on pure logic:
posted by muddgirl at 7:30 AM on April 15, 2015
"Then Cheryl whispered in Albert’s ear the month — and only the month — of her birthday. To Bernard, she whispered the day, and only the day."IE, Cheryl didn't whisper to Albert "I was born in the month of July... Bernard couldn't possibly deduce the month!"
posted by muddgirl at 7:30 AM on April 15, 2015
I'm having (possibly spurious) issues with how/in what sense A initially knows that B doesn't know, and it appears I'm not alone.But the logic doesn't stop there. What if Albert is told that Bernard doesn't know, but Bernard believes that Albert deduced it? Bernard knows the birthday is on the 16th and deduces that it must be July 16. But Albert doesn't know that Bernard has ruled out the month of May. If Albert was told the birthday is in May, he will deduce that Bernard was told it was on the 19th, since that is the only unique day in May. So Albert and Bernard both believe they know. Albert thinks it is May 19 and Bernard thinks it is July 16. But they are both wrong: it is May 16. There are probably more possibilities.
posted by eruonna at 9:58 AM on April 15, 2015
For Persi Diaconis’ Next Magic Trick …
posted by jeffburdges at 12:41 PM on April 15, 2015 [2 favorites]
posted by jeffburdges at 12:41 PM on April 15, 2015 [2 favorites]
That article deserves its own FPP!
posted by muddgirl at 12:49 PM on April 15, 2015 [1 favorite]
posted by muddgirl at 12:49 PM on April 15, 2015 [1 favorite]
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This thread has been archived and is closed to new comments
The comments of "that's not the right solution" gave me a nice chuckle, though. I wonder if they are the same people who question the Monty Hall solution and claim that it's always 50%. Like, there are 20 people in the world whose sole job is telling people that obvious solutions are incorrect. Somebody call the Radiolab guys, I have an idea for a show.
posted by (Arsenio) Hall and (Warren) Oates at 10:38 AM on April 14, 2015 [4 favorites]