I am sure many of you have seen this as it has gone viral on every social media platform and has appeared on all major US news sites

Quote :

"The question first appeared on April 8, as part of the Singapore and Asian Schools Math Olympiads contest. It was posted online Friday by a Singaporean television presenter and quickly went viral — perhaps because the problem was initially misidentified as one intended for 10- and 11-year-olds. As the problem spread far and wide, it became a bit of a joke. Truthfully, we blame no one for choosing to laugh instead of crying out of frustration. The question is actually from a test given to students who are sophomores or juniors in high school — not middle school kids. And it comes deep into the exam and is one of the more difficult problems that students encounter. “Being Question 24 out of 25 questions, this is a difficult question meant to sift out the better students,” Math Olympiads organizers wrote in a statement. “SASMO contests target the top 40% of the student population and the standards of most questions are just high enough to stretch the students.”"

Singapore places 1st or 2nd in the PISA rankings every year for math; US placed 36 out of 65 countries last time. For those not in the know: https://en.wikipedia.org/wiki/Programme_for_International_Student_Assessment#Results


Solutions abound and are easily found with a 2 sec google search, but I want to solve it myself. I am nearly there, just haven't been able to devote a solid 10-15 minutes to it yet.

Have at it!

[Edited on April 15, 2015 at 12:56 PM. Reason : ]

4/15/2015 12:55:15 PM

I haven't seen it yet. But I'm pretty sure I know the answer. But I don't want to post it and look stupid if I'm wrong.

4/15/2015 1:11:35 PM

It's not a math problem. It's a logic problem.

4/15/2015 1:19:01 PM

It's July 16th...which is coincidentally my birthday.

4/15/2015 1:19:59 PM

Yay, that's what I thought too.

4/15/2015 1:20:42 PM

Oh...and let me tell you why:

Albert knows the month.

Bernard knows the day.

Since Bernard doesn't know initially...that means we can rule out May 19th or June 18th...because they are the only unique days of the options.

Then for Albert to know that Bernard does not know, he must have been told July or August, because it rules out the 18th and 19th.

So Bernard now knows that Albert has figured out that it's either July or August. Which leaves the numbers 15, 16, and 17. It can't be 14, because then neither would really know (and it says someone knows).

So that means its either July 16th, August 15th, or August 17. Since Albert only knows the month, and he now knows the date, then it must be July 16th.

[Edited on April 15, 2015 at 1:31 PM. Reason : .]

4/15/2015 1:30:37 PM

^That's what I was thinking too. I was working on explaining how I got to that answer, but I think you're explanation is clearer than mine would've been.

And yeah - not math related at all. Just logic or critical thinking.

4/15/2015 1:34:57 PM

Albert knows the month. When he says that Bernard doesn't know the Birthday, it's because he knows the month does not contain a unique data. That means that ALL of May and June are ruled out. Because of the 18th/19th.

So now we're just down to July and August. Bernard didn't know at first, because it was a duplicate number. Now that May and June are eliminated, he can pick the right date because he knows the unique date left. That means July and August 14th are eliminated.

Now you just have July 16th, August 15th and August 17th.

Since Albert then got the correct date by knowing the month, the two August dates are eliminated, meaning the answer is July 16th.

[Edited on April 15, 2015 at 1:41 PM. Reason : ^^ whatever i got sidetracked before I posted. ]

4/15/2015 1:41:11 PM

I suppose this isn't quite mathematics, but it's pretty damned close. it's exactly the kind of reasoning employed in mathematical proofs.

also, the boundary of what constitutes "mathematics" is pretty fuzzy. there are plenty of subjects that involve numbers only minimally, if at all (i.e. geometry, set theory, logic) which are nevertheless active areas of mathematical research.

4/15/2015 1:42:46 PM

Agreed it is a logic problem, but since it appeared in the "Math Olympiad", I called it a math problem.

4/15/2015 1:43:25 PM

Quote :

"So what makes Singapore so good at a subject with which America's students have routinely struggled? Singapore's math instruction focuses heavily on mastery over rote memorization. Math students on the small island nation perform well because they understand the material deeply—not because they are studying for a specific test. Thus, they react well when "curveballs" are thrown at them in the form of confusing math questions. Furthermore, the instruction of "Singapore Math" (http://www.singaporemath.com/Media_s/13.htm) —as it's dubbed in the U.S. —uses a "layered" approach aimed at facilitating comprehension. Students digest the subject in stages, from the concrete to the pictorial and eventually to the abstract. This leads to conceptual understanding rather than numerical regurgitation: It's not just about getting the correct answer, but also about explaining one's thought processes. U.S. students have made strides in math proficiency in recent years, but they still lag behind many of their peers internationally, falling at the middle of the pack in global rankings. In the same PISA report the U.S. placed 35th out of 64 countries in math."

The Singaporean curriculum is apparently being adopted in US schools: http://www.singaporemath.com

4/15/2015 2:01:17 PM

Sounds like common core.

4/15/2015 2:21:58 PM

^^It is increasingly popular in private schools IIRC.

^It was one of many inspirations for the Common Core IIRC.

4/15/2015 2:32:04 PM

OK so. The one thing I'm having trouble understanding. Probably extremely stupid, but it's getting in my way. Bernard does not know but knows the day of month, which immediately rules out the unique dates, June 18 and May 19. Got it. Bernard knows this rules out June, since there's only one other date in June, and Albert doesn't know. Got it.

Why does this rule out May?? There are two other dates in May. Both are duplicated in either July or August. So to my way of seeing things, since it's not the 18th or 19th, that leaves Bernard with the possibilites 14, 15, 16, and 17. Albert could know it was May but still doesn't know whether it's the 15th or 16th. Therefore Albert's initial statement, to me, only eliminates June and doesn't actually help Bernard. And with June still off the table but May on, then you have duplicate dates on 14, 15, *and* 16, which means the answer would be August 17, which was my initial answer. Tell me where I went wrong here.

[Edited on April 15, 2015 at 3:14 PM. Reason : a]

4/15/2015 3:13:32 PM

Albert KNOWS that Bernard doesn't know the answer. If Albert knew the month was May then Bernard COULD know that the date was the 19th. If Bernard knows the date is the 19th than he knows the whole answer.

Since Albert says he KNOWS that Bernard doesn't immediately know the answer, Bernard can deduce that Albert was not given the month of May.

4/15/2015 3:18:36 PM

these are fun, but lame for scrolling down and finding the answer before figuring it out for myself

4/15/2015 3:54:52 PM

Its 'cool' that a school system teaches kids how to solve such problems. However its not practical.

What's the point on sitting on a lonesome island and knowing how to solve impractical problems on paper but not applying it to make that cash?

Who cares?

BITCH

I GOT THE JOB

4/15/2015 4:17:00 PM

Quote :

"these are fun, but lame for scrolling down and finding the answer before figuring it out for myself"

- if someone posts a puzzle on tww, there is a 100% probability that people will discuss it and post the answer in the thread

- what did you really expect beyond the 1st post?

- the answer is not a single number, rather a whole logical thought process, so you can't know the answer by a single unintentional glance

- even if you did see the birthdate, it is a date, so it doesn't tell you by magic how the answer was arrived at, which means you can and should still do it yourself

4/15/2015 4:32:30 PM

MORE!

4/15/2015 6:04:57 PM

Sounds like Cheryl's an annoying bitch, they should drop her before she traps one of them into a hellish relationship

4/15/2015 6:26:45 PM

^yeah seriously. who responds to "when's your birthday" with a fucking riddle? i wouldn't wanna be friends with her.

4/15/2015 8:09:33 PM

she should have said "I'll fuck the first one of you who guesses my birthday," because then they'd try to mislead each other, and the problem would become far more challenging. you'd have to use game theory to solve this case, I think.

4/15/2015 8:18:35 PM

i'm with richthofen

I too don't see why ruling out 19 rules out the rest of May. I do understand why June is ruled out, but that's under a different logic: B knows that it's not June 17 because A knows June 18th is out of the running and would immediately choose the 17th had "June" been whispered to him.

4/15/2015 10:18:06 PM

This little interplay between Al and Bernie is throwing me off, are they working together and communicating with each other, or are they competing?

How do they know what the other doesn't know without just knowing the answer?

[Edited on April 16, 2015 at 12:27 AM. Reason : post count palindrome]

4/16/2015 12:25:40 AM

if I know qntmfred has told you shoot's gender, then I can be sure you haven't figured out his identity on that basis alone, because he might be dropdeadkate or BridgetSPK, or he might be Ernie or amac884. his gender (no matter which it is) is not sufficient info to identify him.

but if YOU know that I'VE also failed to identify him based solely on, say, the first letter of his real username, then you can conclude that, for example, he can't be zorthage (because zorthage is the only user on TWW whose username starts with Z, so if qntmfred had said "His name starts with Z," I'd have him.) so you can then use my lack of certainty to narrow your own choices down.

4/16/2015 12:34:29 AM

I still don't see how this is math

[Edited on April 16, 2015 at 12:44 AM. Reason : ]

4/16/2015 12:41:23 AM

because Albert knows the month, and none of the possible days in that particular month are unique to that month.

if any of the days in that month were unique to that month (as, for example, May 19th is the only 19th) then, if the month were May, it's possible that Cheryl told Bernard "It's the 19th," in which case Bernard would knjow.

Albert is saying that the correct month doesn't contain any days like that.

I fucked that ^^ up initially


[Edited on April 16, 2015 at 12:47 AM. Reason : ewgr]

4/16/2015 12:44:13 AM

Quote :

"i'm with richthofen I too don't see why ruling out 19 rules out the rest of May. I do understand why June is ruled out, but that's under a different logic: B knows that it's not June 17 because A knows June 18th is out of the running and would immediately choose the 17th had "June" been whispered to him. "

19 isn't ruled out, Albert only knows the month. All Albert is saying is that "it's not a month that has a uniquely identifiable day". Albert isn't giving any more info than that with the first line.

4/16/2015 12:47:48 AM

I think the biggest challenge with this problem is realizing that the people in the problem can rule out things easily that we as the outside observer can't.

Working backward from the solution because it's easier to explain that way, Albert was told "July" so he knows right away that Bernard doesn't know, since the dates in July are also in other months, that's why he says he knows Bernard doesn't know because the only way Bernard would know is if it was May 19 or June 18.

Bernard was told 16, so he knows it's either May or July. Once he is aware that Albert knows he doesn't know (which rules out May and June) then he knows it has to be July or August, and since there is no option for August 16 it has to be July 16.

[Edited on April 16, 2015 at 12:58 AM. Reason : Although still my first solution to the problem would be to rule out Cheryl as a friend]

4/16/2015 12:58:12 AM

goalie lax nailed it. it's strict logic. confounded, but strict

4/16/2015 12:58:50 AM

it's all about that Louis Logic

4/16/2015 1:08:57 AM

it's kinda like the joke about 3 logicians who walk into a bar

3 logicians walk into a bar the bartender says
"Do you all want a beer"
First Logician says "I don't know"
Second Logician says "I don't know"
Third Logician says "Yes we all want a beer"

Since the other two didn't say no the third could imply they wanted a beer and since he himself wanted a beer he could answer the question affirmatively.

So since May 19th and June 18th were unique day numbers and since Albert stated that he knew that Bernard didn't know the birth date it couldn't be either of the two unique dates which knocks those two months off. From there we can deduce that it had to be a date that had a duplicate day number and either July or August for the month. Since after Albert made his statement Bernard knew it wasn't May or June, and then given the fact that Bernard figured it out we can deduce that it has to be a date that has a day number common between the ruled out months and the remaining months which rules out July and August 14th because if it was the 14th of either month Bernard couldn't know for sure. At this point the possibilities are July 16th August 15th and August 17th. Since Albert could figure it out from Bernard's statement the month has to be July because if it was August Albert couldn't know for sure which day it was. The only day in July we can't rule out is the 16th based on our previous deductions. Therefore her birth date is July 16th.

4/16/2015 1:31:13 AM

This is the same concept of this OP problem, except there is no one to give you a question or questions and you have to ask yourself what happening here about the whats and whys. I will say its White to move, and its only needed that you know how to chess pieces move and you need some INSANE logic thereafter hahahaha. I guess if you are not any good at chess there is a 99.99999999% chance you will not solve this problem. Good luck.

This is a theroectical Rook endgame that any decent chess player show know like the back of his or her hand.

What's the point of knowing this? For funnsies!

4/16/2015 8:20:40 AM

USA! USA!

4/16/2015 5:20:03 PM

This is not math, your argument is invalid.

4/16/2015 5:26:52 PM

^^^ Since that didn't actually ask a question, I'm gonna go ahead and solve it.

There are 5 pieces on the chess board.

Boom, logic puzzle solved.

4/16/2015 6:03:28 PM

Hahahaha

4/16/2015 6:10:00 PM

nevermind, figured it out.

[Edited on April 16, 2015 at 8:49 PM. Reason : add another note]

4/16/2015 8:37:57 PM

I'm not a chess guy by any stretch, but the iPhone app "Mate in 1" and "Mate in 2" are amazing for exercising your problem solving skills.
Fun?.... Eh when you get a really super hard one right it makes up for the frustration.

It's pretty much metroid

4/20/2015 8:45:32 PM

7/18/2015 6:46:56 AM

2

7/18/2015 7:06:23 AM

3

7/18/2015 9:48:32 AM

2

7/18/2015 9:55:03 AM

box 2

7/18/2015 10:06:40 AM

Quote :

"3"

3 is the true statement, which makes the car in box 2

7/18/2015 10:13:18 AM

why would anyone waste their time on this

7/19/2015 2:31:39 PM

like why the fuck is Cheryl such a god damn bitch that she can't just tell someone her birthday

and why are we spending time on a hypothetical and ridiculous situation

you could have posted like 100 smilies in the meantime

7/19/2015 2:34:19 PM

Because some people actually enjoy using their brains for something other than collecting bong residue?

And before you go ahead and post, "oh look, another bitchy post from el nacho", like you always do, I just want to point out the fact that I'm responding to yet another bitchy (double) post by you. You're more negative than I am, way dumber, and actually think that posting 100 icons would somehow be a benefit to anything other than your post count. Why haven't you done the world a favor and ODed on something yet?

7/19/2015 3:15:14 PM

fucking shut the hell up and die

7/19/2015 3:44:10 PM

wanna talk some god damn shit

THEN COME FUCKING SAY IT TO MY GOD DAMN FACE

7/19/2015 3:44:31 PM