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When Is Cheryl's Birthday?

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Re: When Is Cheryl's Birthday?

#61

Post by andrewprock »

stephen_g wrote: post #60
andrewprock wrote: post #13

Unfortunately, there are a number of rather curious, and culturally specific, assumptions one must make about the problem. The real puzzles are: 1. "Why did Albert speak first?" 2. "Why did he speak in such cryptic language?"

Maybe I'm missing something, but we know exactly what Bernard would have said first from statement 2. He says, "At first I didn't know", so all he could have said if he had spoken first would have been "I don't know when the birthday is". Then Albert would have said, "I don't know when the birthday is, and I knew that Bernard couldn't have". So the problem is unchanged regardless of who speaks first. It also doesn't…

IIRC, if Bernard speaks first, then the correct answer is August 17.

Re: When Is Cheryl's Birthday?

#62

Post by stephen_g »

anigbrowl wrote: post #32
andrewprock wrote: post #13

Unfortunately, there are a number of rather curious, and culturally specific, assumptions one must make about the problem. The real puzzles are: 1. "Why did Albert speak first?" 2. "Why did he speak in such cryptic language?"

These are actually valid questions and you shouldn't be downvoted. The standard interpretation of the problem is highly questionable; Albert's initial remark is not actually dispositive to Bernhard, because if Bernhard had the 19 May date he would know the correct answer immediately without needing Albert to say anything. The suggestion that Albert's first statement necessarily eliminates all dates in May is false, a…

Your objection doesn't make sense. The fact that Albert can make the statement relies on the fact that he was given a month that rules out Bernard being given a unique date, such as the 19th, otherwise Albert would have to say, "I don't know when the birthday is but perhaps Bernard does" and the problem would be different.

Albert knows the month, and his statement, which translates directly to "given the month I know, it is not possible for Albert to independently determine the date" certainly does rule out the two months.

Re: When Is Cheryl's Birthday?

#64

Post by baddox »

codeulike wrote: post #49
baddox wrote: post #46

Earlier quoted context omitted.

Why do you say that is cryptic? I can't think of a clearer or plainer way to express that fact.

Trust me, its cryptic to most people, and that's why this puzzle has gone viral round the world in an omg-singapore-schoolkids-can-do-this-insane-puzzle kind of way.

Why do you suspect the crypticness of the puzzle's language is the problem, rather than the fact that a large portion of people haven't studied basic logic and are thus unable to complete basic logic puzzles?

Re: When Is Cheryl's Birthday?

#65

Post by stephen_g »

andrewprock wrote: post #61
stephen_g wrote: post #60

Earlier quoted context omitted.

Maybe I'm missing something, but we know exactly what Bernard would have said first from statement 2. He says, "At first I didn't know", so all he could have said if he had spoken first would have been "I don't know when the birthday is". Then Albert would have said, "I don't know when the birthday is, and I knew that Bernard couldn't have". So the problem is unchanged regardless of who speaks first. It also doesn't…

IIRC, if Bernard speaks first, then the correct answer is August 17.

That doesn't make any sense to me. Can you post exactly the sequence of statements if Bernard speaks first?

Simply reordering the questions does not make sense, so I can't see it happening any way other than what I posted, which shows that it wouldn't change anything.

Re: When Is Cheryl's Birthday?

#67

Post by vacri »

logicallee wrote: post #36
gkoberger wrote: post #18

Maybe I'm missing something, but the "hard" part of this problem is figuring on the trick. Once you know that, it becomes relatively easy – and you can't use a program to figure out the trick.

I don't know, can code like this reason about knowledge-about-knowledge in general? For example, can a version of the code be used to solve the 'hardest puzzle' - https://xkcd.com/blue_eyes.html (solution: https://xkcd.com/solution.html ) ?

I find the problems with puzzles like these is not the rules, but the ridiculously contrived situations. Why do these entities that function like inert logic gates have to be human? It means that the question has to have silly rule placed on silly rule in order to keep the contrived situation afloat. It means I end up thinking of ways for the mute, inert people to free themselves from the island (who is feeding them? Are there trees to build a raft? etc), rather than 'play by the rules'.

Re: When Is Cheryl's Birthday?

#68

Post by baddox »

andrewprock wrote: post #58
baddox wrote: post #47

Earlier quoted context omitted.

Assuming that the problem is posed and understood as an artificial puzzle (rather than a real scenario with real people), what reason would there be to question how they know? Of course you're supposed to assume they know. It's a puzzle, and someone is telling you precisely what you're to assume.

On the contrary, there are many unspoken things one must assume to solve this puzzle "correctly"; that Albert and Bernard are rational, honest, cooperating, and have a certain penchant for communicating novel inferences they make instead of just blurting out "we don't know" out of boredom, laziness, or frustration.

To me, all those things are very readily inferred from the fact that the problem is being posed as a logic puzzle.

Re: When Is Cheryl's Birthday?

#69

Post by baddox »

zhte415 wrote: post #52

The problem with this problem, the way it was originally put, was the utterly confusing English masked into a logic problem. Write your specifications clearly, and then it does not become an internationally shared 'problem' to solve. [I work with insanely documented specifications just like this, year after year. Not putting a problem clearly is not something to aspire to.]

Why do you think that confusion over the English description is more to blame than the difficulties many people face with logic puzzles?

Re: When Is Cheryl's Birthday?

#70

Post by gurkendoktor »

baddox wrote: post #46
codeulike wrote: post #44

Earlier quoted context omitted.

Its understanding what the question actually means when it says things like 'Bernard: At first I don't know when Cheryl's birthday is, but I know now.' ... this is actually a cryptic coding of the rules of the puzzle. If you properly understand those rules and convert them to code (as in the OP) then searching the possible answers for a match is trivial.

Why do you say that is cryptic? I can't think of a clearer or plainer way to express that fact.

Not a native speaker, but just the fact that the first half of the sentence is written in the present tense made my brain stumble.

Which is probably intended, as otherwise I would have thought he meant to say "before Cheryl had told me, I didn't know".

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