rd-aaron has it. I disagree with Polak's solution.
Spoiler!
Cheryl tells Albert the month she was born. She tells Bernard the day.
Neither Albert or Bernard can figure it out from the info she gave.
When Bernard hears Albert say that "I don't know, and I know Bernard doesn't either", then Bernard knows the answer.
From this statement we know that it cannot be June 18 or May 19. (Because, Bernard, knowing the day would have figured that out on the spot as both 18 and 19 are unique in the puzzle.)
At this point, Bernard already knows is not May or June (we don't know, but that, but we can reason it out from Albert's statement that "I don't know, and neither does Bernard.) Albert's statement gives us some extra info that we didn't know in the beginning. Now we ALL know its NOT May or June.
That leaves July and August - both of which have days in common, except for the 16th.
Bernard can then figure out that the only non-repeated day is the 16th, so her birthday must be July 16.
And when Albert hears Bernard say that he knows (based on Albert's previous statement), that gives Albert the missing piece of the puzzle too.
I think the question is poorly worded, grammatically speaking. Kind of a mean thing to do to kids in a high-pressure test situation. Its not really clear that Bernard and Albert are able to hear each other. But then again, maybe that's a cultural assumption in Singapore?
Last edited by annasuave; 04-13-2015 at 03:43 PM.
Reason: for saying Albert when I meant Bernard
rd-aaron has it. I disagree with Polak's solution.
Spoiler!
Cheryl tells Albert the month she was born. She tells Bernard the day.
Neither Albert or Bernard can figure it out from the info she gave.
When Bernard hears Albert say that "I don't know, and I know Albert doesn't either", then Bernard knows the answer.
From this statement we know that it cannot be June 18 or May 19. (Because, Albert, knowing the day would have figured that out on the spot as both 18 and 19 are unique in the puzzle.)
At this point, Bernard (knowing the month) knows its NOT May or June.
That leaves July and August - both of which have days in common, except for the 16th.
Bernard can then figure out that the only non-repeated day is the 16th, so her birthday must be July 16.
I think the question is poorly worded, grammatically speaking. Kind of a mean thing to do to kids in a high-pressure test situation. Its not really clear that Bernard and Albert are able to hear each other. But then again, maybe that's a cultural assumption in Singapore?
You've done what I did a million times and flipped what Albert and Bernard know.
I think the question is poorly worded, grammatically speaking.
That's true. Seems like a lot of preambles are missing which require the students to guess. But once you make the connection of what they know or how they come about knowing them, the question isn't as hard as it first appears.
No no, nothing was meant from that. I was just joking around.
Singapore's primary languages are English and Mandarin. Almost everyone has an English name.
As long as we're cool...
Looking at the most popular baby names there right now, it's sad to see they are being afflicted by the same Jayden, Aiden, Cayden, Brayden names that we are here.
Anyway, I think this just goes to show that I don't have the attention span to even attempt these logic questions.
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Originally Posted by darklord700
There's a second answer which Polak got depedning on the assumption you make.
Spoiler!
Alberta heard Bernard say Bernard doesn't know, so Alberta knows it cannot be May 19 and June 18. It also cannot be June 17 otherwise Albert would have known at that stage.
Bernard at that stage knows the remaining possible dates are:
May 15, 16
July 14, 16
August, 14, 15 & 17
And since Bernard declares he knows, it is only possible if Cheryl tells Bernard the 17th date, so August 17 is also the correct answer.
You're wrong dude.
You don't have to make any assumptions.
Spoiler!
Alberta heard Bernard say Bernard doesn't know, so Alberta knows it cannot be May 19 and June 18. It also cannot be June 17 otherwise Albert would have known at that stage.
This part is neither stated, nor necesary to the question, and you're conclusion from it is incorrect.
Albert knows the month, and he says he knows bernard doesn't know.
There are two months that have unique days (May is the only month with 19, June is the only month with 18) By saying he knows Bernand doesn't know the birthday, he is saying that it cannot be in a month with a unique day, so it Must be in Either July or August.
Bernard at that stage knows the remaining possible dates are:
May 15, 16 July 14, 16 August, 14, 15 & 17
Nope Bernard now knows the reamiing dates are the 5 in July and August.
And since Bernard declares he knows, it is only possible if Cheryl tells Bernard the 17th date, so August 17 is also the correct answer.
Nope again, Bernard now knows becasue tehre are three unique daets 15, 16 & 17. And when he says he knows the date, then Albert can eliminate the two with 14 Leaving July16, Aug 15&17.
Albert already knows the month, so when he says he knows that means it has to be a uniqe month in that set, which is July.
Therefore, July 16.
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Somewhat related - does anyone else remember the logic puzzles that Thrasher Magazine used to publish? From the spotty clues given, you had to figure out who borrowed who's skate, who ate who's lunch, and who was making time with So&So's Betty.
First statement eliminates May and June as they have singular dates, 18 and 19.
July14 July 16
Aug14 Aug15 Aug17
Second statement eliminates the date of the 14th as it is duplicated.
July16
Aug15 Aug16
At this point we are back to eliminating the month and since there is only one date in July it has to be July 16th. Otherwise how do we determine if it is the 15 or 17?
Just wait until they ask her how much she weighs
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This isn't a hard question actually. But normally, it's hard to comprehend how Albert could know that Bernard doesn't know. But once you get past that stage the process of elimination isn't terribly difficult. In an exam situation that's different though.
If the question is worded as follows, the logical deduction shouldn't be too difficult.
Alberta: After Cheryl told him the month, immediately knows that Bernard doesn't know Cheryl's birthday.
Bernard: After Albert told Bernard Albert doesn't know Cheryl's birthday and with that information, Bernard now knows Chreyl's birthday.
Last edited by darklord700; 04-14-2015 at 08:27 AM.
First statement eliminates May and June as they have singular dates, 18 and 19.
July14 July 16
Aug14 Aug15 Aug17
Second statement eliminates the date of the 14th as it is duplicated.
July16
Aug15 Aug16
At this point we are back to eliminating the month and since there is only one date in July it has to be July 16th. Otherwise how do we determine if it is the 15 or 17?
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