MATH: How can you figure this out?

[Bird222]

http://www.msn.com/en-us/news/us/th...0wHo?ocid=mailsignout&fullscreen=true#image=1

 

[DannyBoy]

I'll tell you on the 16th July.

 

[Ferzerp]

That isn't "math". That's a logic problem.

The first information given rules out May and June because if the month is either of those, then the second person could know the date (only months with 18 and 19).

Now that I've gotten you started, you should be able to figure out the rest.

 

[UncleWai]

It can't be may 19 or june 18 because Bernard will know the bday right away.
So the date was either 14, 15, 16, 17.
Since Albert knows the exact month (either july or august so far) he can conclude that Bernard wouldnt know right away because it wasn't may 19 or june 18.
Bernard then knows the month was either July or August.
We can rule out 14 because it shows up in july and august.
Bernard at this stage would know the answer already because 15 16 17 only showed up once in july or august.

As for Albert, he could only be certain is if he was told the month is July, hence July 16.
I

 

[Ferzerp]

Or you can just give it away and not let the guy think

 

[dank69]

Albert knows month. When he says he knows Bernard doesn't know as well this tells Bernard that the month must be July or August because if it were May or June there would be a possibility that the day was 18 or 19 and Bernard would know the whole date.

Now that Bernard knows that the month must be July or August he says he knows the whole date. This means the day can't be 14.

Then Albert says he knows the full date so the month must be July. If it were August he still wouldn't know if it was 15 or 17.

 

[DrPizza]

That'll make a nice extra credit problem (obfuscated though - dates, names, and event changed to make it ungoogleable.)

 

[dabuddha]

June 17

 

[destrekor]

August 17.

Bernard knows it is 17, but not sure which month.

Albert knows that it is August, but not the day.

Bernard figures that is cannot be June 17, because is Albert knew it was June, he should know immediately that it is June 17th because clearly it would not be the 18th or Bernard would have known immediately. So knowing that Albert did not immediately jump to the only other valid day in June by having known only that it is in June, that leaves Bernard to know for sure that it is August 17.

Albert, now knowing that Bernard now knows only because he could tell Albert did not know for certain, makes it clear to Albert that there must have only been two possibilities for Bernard to be so certain: June 17 or August 17. If it had been 18, Bernard would have known immediately, and thus, if Albert knew it was June, Albert should have figured this out immediately. Thus, Albert finds it likely that Bernard can safely assume it is only one other choice, and having become certain, Albert now is also clued into the only clear choice, August 17.

I probably explained the competing logic terribly, but I feel that is the correct answer.

 

[pete6032]

Honestly Cherly is a little bitch for not just saying what her birthday is. Also Albert and Bernard should just tell each other what Cheryl said instead of beating around the bush about it.

 

[destrekor]

I sort of retract my answer, because the school that created it posted the answer.

It can be found here, with full explanation. They tweeted a picture with the logic and solution.

I guess part of their answer hinges on completely discarding May, which frankly makes no sense to me. So Albert knows Bernard was not told the 19th, but Albert would not know which of the other two dates in May, and Bernard, knowing it is either the 15th or 16th, is not given any proper clue.

May should not be thrown out of the solutions, IMHO.

 

[Carson Dyle]

May should not be thrown out of the solutions, IMHO.

May is discarded for exactly the same reason that June is discarded. May and June contain the only two dates that are unique - 19 (May) and 18 (June). If Albert had been told either May or June, then there's a possibility that Bernard would know the birthday just by knowing the day. He says that isn't so, therefore both months can be eliminated.

 

[dank69]

I sort of retract my answer, because the school that created it posted the answer.

It can be found here, with full explanation. They tweeted a picture with the logic and solution.

I guess part of their answer hinges on completely discarding May, which frankly makes no sense to me. So Albert knows Bernard was not told the 19th, but Albert would not know which of the other two dates in May, and Bernard, knowing it is either the 15th or 16th, is not given any proper clue.

May should not be thrown out of the solutions, IMHO.

If Albert was told May he could not have stated that Bernard could not know the answer.

 

[destrekor]

May is discarded for exactly the same reason that June is discarded. May and June contain the only two dates that are unique - 19 (May) and 18 (June). If Albert had been told either May or June, then there's a possibility that Bernard would know the birthday just by knowing the day. He says that isn't so, therefore both months can be eliminated.

Again, that still only makes sense for June. June only has 2 days, May has 3.

So by knowing it is NOT May 19th, that doesn't preclude it from being the other two possibilities. June is easy to discard because without it being June 18, Albert would know if it were June. If Albert knows it is May, all he knows for sure is it cannot be May 19th, because Bernard would know. Bernard can know it is the 15th or 16th and not know, and Albert can know it is May and can only say for sure it is not the 19th.

That the official answer (by the school) immediately rejects May is a little confusing. I think that is a false premise and skews the rest of the solution.

 

[destrekor]

If Albert was told May he could not have stated that Bernard could not know the answer.

I see, semantics. I was going on the assumption that if one knew, he would be showing this or saying it to the other, without revealing the answer.

There's the "possibility" of it being the 18th or 19th and Bernard knowing all along, I was discounting that idea and going for a more literal approach. He does not know, thus, it is not the 18th or 19th.

 

[gorobei]

i got june 17.

it doesnt say which guy got the month and which got the day.
in order to know that the other guy cant solve it you must have the day. if you have the month there are at least 2 or 3 options for each month.
therefore albert has the date. if he still doesnt know then it cant be 18 or 19.
that leaves 14 15 16 17.
if bernard knows the month, the only way he can know the date is if there is only one option in that month. therefore since 18 has been eliminated only june can give bernard certainty.

 

[Carson Dyle]

I see, semantics. I was going on the assumption that if one knew, he would be showing this or saying it to the other, without revealing the answer.

Always wondered why kids had so bloody much trouble with so-called word problems in school. Never really saw how the gears turned (or failed to) until now.

There's the "possibility" of it being the 18th or 19th and Bernard knowing all along, I was discounting that idea and going for a more literal approach. He does not know, thus, it is not the 18th or 19th.

Which is actually correct. And from that you should have deduced that it's neither May nor June.

 

[dank69]

i got june 17.

it doesnt say which guy got the month and which got the day.
in order to know that the other guy cant solve it you must have the day. if you have the month there are at least 2 or 3 options for each month.
therefore albert has the date. if he still doesnt know then it cant be 18 or 19.
that leaves 14 15 16 17.
if bernard knows the month, the only way he can know the date is if there is only one option in that month. therefore since 18 has been eliminated only june can give bernard certainty.

Respectively tells you who got what.

 

[gorobei]

Respectively tells you who got what.

yeah i just saw that part, i was going off the msn article and missed that bit in the original image.

the official answer works then.

 

[destrekor]

Always wondered why kids had so bloody much trouble with so-called word problems in school. Never really saw how the gears turned (or failed to) until now.

I actually did just fine in reading and word problems, thank you very much. Those were among my strongest on the ACT.

I has reading skillz. I guess I sort of skimmed or glossed over that part.

Which is actually correct. And from that you should have deduced that it's neither May nor June.

And from that, I did deduce that, once I had understood the problem as it was intended. At first, I did not reach that conclusion, as I thought you had seen, because I misinterpreted the situation.


It's all good here now. Move along.

 

[cubby1223]

The modern solution to that puzzle is:

Bernard checked Cheryl's facebook feed and noticed she received happy birthday messages on that exact date of the previous year

 

[Rakehellion]

That isn't "math". That's a logic problem.

Logic is a type of math.

 

[Ferzerp]

I knew when I posted that, that someone would be a pedant about it.

 

[cubby1223]

The answer should be June 17.

The thing that is stupid with this problem is it's not a normal flow of conversation. It projects an image that these lines are being said one after the other, when in reality the flow is more like:


Cheryl then tells Albert & Bernard the month & day

<Albert and Bernard separately study all the possibilities for a few minutes>
Albert: I don't know her b-day, but I can deduce Bernard does not know
<Albert and Bernard study all the possibilities for a few more minutes>
Bernard: At first I didn't know but now I know
<Albert studis all the possibilities for a few more minutes>
Albert: I know now


If worded like that it leads people towards the proper answer.

 

[gorcorps]

I got July 16th

any other answer is from a dumb dumb head