When Is Cheryl's Birthday? • Hacker News Board

Re: When Is Cheryl's Birthday?

#71

Post by zhte415 » Sat, Apr 25, 2015, 9:15 AM UTC

baddox wrote: post #69

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?

I do not make a comparison to 'difficulties many people face with logic problems' and did not make an assertion that many people face difficulties with logic puzzles.

Getting back to the article: the problem is worded so badly it should be sent back to the author to more coherently express what they think. Specifications, etc...

Re: When Is Cheryl's Birthday?

#72

Post by codeulike » Sat, Apr 25, 2015, 9:35 AM UTC

baddox wrote: post #64

codeulike wrote: post #49

Earlier quoted context omitted.

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?

Firstly, someone reading the puzzle needs to grok that some of the day-numbers are unique across the months (e.g 18) and some are not (14). Then they need to grasp the basic dynamic on the situation, e.g. that if Cheryl's birthday had been May 19 then Bernard would have known straight away.

If you dont initially grasp the above then Albert's initial declaration "I don't know when Cheryl's birthday is" just seems to be a redundant statement that doesn't offer any information. And thats just the first hurdle of the puzzle.

A lot of people hate maths-questions-stated-as-stories, even simple ones ("There are several chickens and rabbits in a cage (with no other types of animals). There are 72 heads and 200 feet inside the cage. How many chickens are there, and how many rabbits?" etc etc) so to people like that, this Cheryl-birthday problem initialy presents as hopelessly cryptic.

Re: When Is Cheryl's Birthday?

#73

Post by tomp » Sat, Apr 25, 2015, 9:39 AM UTC

For the more mathematically minded readers, here's a harder version of the problem:

http://jdh.hamkins.org/transfinite-epistemic-logic-puzzle-ch...

Re: When Is Cheryl's Birthday?

#74

Post by stephen_g » Sat, Apr 25, 2015, 9:41 AM UTC

gurkendoktor wrote: post #70

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.

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".

Interesting. As a native English speaker, I didn't even consider "before Cheryl had told me, I did not know" as a possible interpretation, just from the way the conversation flows but also because it goes without saying and wouldn't add anything.

In the context of Albert's statement though, it couldn't mean that - Albert's statement is saying that Bernard does not have enough information to determine the date just based on what Cheryl told him, so in saying "at first I did not know, but now I know", the only difference between "at first" and "now" is Albert speaking.

So Bernard's comment could only mean, "Based on what Cheryl told me, I did not know what the birthday was, but given the extra information I have as a result of Albert's statement, now I know"

Re: When Is Cheryl's Birthday?

#75

Post by Gigablah » Sat, Apr 25, 2015, 9:43 AM UTC

john_butts wrote: post #15

1. HN comment about some aspect of fizzbuzz or whatever. Not how to solve fizzbuzz or whatever; rather, some insight into how people solve problems, which is the interesting part of the question. 2. Two dozen oblivious nerds tell u how to do it in 20 characters of perl

Are you offended that people are sharing their knowledge?

Re: When Is Cheryl's Birthday?

#76

Post by mseebach » Sat, Apr 25, 2015, 9:48 AM UTC

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.

For outsiders, there are two elements to the puzzle: the encoding of the logic problem and the logic problem itself.

People might very well be able to solve even fairly complex logic problems without having been exposed to this tradition of encoding such problems.

The problem is stated as three persons having an odd, but casual conversation. To outsider that's all they're doing and to those the problem is impenetrable. Insiders, however, immediately recognise the informal protocol of logic quizzes that this is not a random casual conversation, it is carefully written to encode just enough information to be solvable as a logic problem. These insiders know to carefully extract (decode) this information. Only then do they solve the logic problem.

The "dishonesty" of the problem, which is confusing to people expecting the problem to be stated honestly, is that the conversation in the problem is entirely contrived, there is no way is would ever happened as part of a real world exchange about birthdays. This is fine for the intendeded reader, school kids trained in this protocol, but in "going viral" it went to a lot of unintended recipients.

Re: When Is Cheryl's Birthday?

#77

Post by codeulike » Sat, Apr 25, 2015, 9:51 AM UTC

mseebach wrote: post #76

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.

For outsiders, there are two elements to the puzzle: the encoding of the logic problem and the logic problem itself. People might very well be able to solve even fairly complex logic problems without having been exposed to this tradition of encoding such problems. The problem is stated as three persons having an odd, but casual conversation. To outsider that's all they're doing and to those the problem is impenetrabl…

Yep, exactly.

Re: When Is Cheryl's Birthday?

#78

Post by stephen_g » Sat, Apr 25, 2015, 10:11 AM UTC

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.]

It's a puzzle - it's supposed to be tricky.

I don't really think it's especially obfuscated though. You just have to think about why people are saying what they say, which is a fairly useful thing to be able to do...

Re: When Is Cheryl's Birthday?

#79

Post by pdpi » Sat, Apr 25, 2015, 10:26 AM UTC

Jach wrote: post #9

ternaryoperator wrote: post #4

Earlier quoted context omitted.

>since it is relatively simple to solve You are overestimating how simple it is.There are more than 1200 comments on the solution on the NYTimes[1] almost all of them arguing that other dates are correct. [1] http://www.nytimes.com/2015/04/15/science/answer-to-the-sing...

It's relatively simple, if you're the kind of person who grasps that 1+1*0 is not 0 under most parsers and under the order of operations implied by e.g. the vector space axioms...

> under the order of operations implied by e.g. the vector space axioms

What, exactly, about vector spaces implies an order of operations?

Re: When Is Cheryl's Birthday?

#80

Post by chongli » Sat, Apr 25, 2015, 10:30 AM UTC

baddox wrote: post #42

ternaryoperator wrote: post #4

Earlier quoted context omitted.

>since it is relatively simple to solve You are overestimating how simple it is.There are more than 1200 comments on the solution on the NYTimes[1] almost all of them arguing that other dates are correct. [1] http://www.nytimes.com/2015/04/15/science/answer-to-the-sing...

It's very simple in the context of logic puzzles. Similarly, the melody of "Ode to Joy" is very simple to play on the piano. That's not to say that there aren't at least 1,200 people unable to play it on the piano. But it is one of the simplest recognizable melodies to play on the piano, and is likely playable by the vast majority of people with a few months of piano lessons.

The hard part is not the logic, it's actually figuring out that this is a logic puzzle that needs to be solved by deduction and not a bunch of nonsense with terrible grammar. To borrow your Ode To Joy example, it's like trying to learn to play the piece after the sheet music had been torn and tattered, burned and stained with coffee. Sure, the music is simple once you get past all of the garbage in your way.

The original version of the puzzle (in the Singapore Math Olympiad) presented the dates in a sparse table format. This little bit of symbolic communication makes it much clearer that the answerer is supposed to cross off the dates by a process of deduction, making the puzzle simple to solve.