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pongo

Can you solve the maths question for Singapore schoolkids that went viral?

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This is one on the same lines as the monk one - years and years ago I was told an amalgam of the two puzzles and it literally took me a year before I understood it with any confidence!

 

The King called the three wisest men in the country to his court to decide who would become his new advisor. He placed a hat on each of their heads, such that each wise man could see all of the other hats, but none of them could see their own. Each hat was either white or blue. The king gave his word to the wise men that at least one of them was wearing a blue hat - in other words, there could be one, two, or three blue hats, but not zero. The king also announced that the contest would be fair to all three men. The wise men were also forbidden to speak to each other. The king declared that whichever man stood up first and announced the color of his own hat would become his new advisor. The wise men sat for a very long time before one stood up and correctly announced the answer. What did he say, and how did he work it out?

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Doh, got it. I was concentrating on the number so much that I forgot Albert already knew the month.

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I can't see how to get from there to the answer.

It's the fact of Bernard then knowing the answer which tells us (and Albert) what it must be.

 

ETA: cross posted

Edited by pongo

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I can't see how to get from there to the answer.

It's the fact of Bernard then knowing the answer which tells us (and Albert) what it must be.

 

ETA: cross posted

 

 

It tells Albert. Albert working it out tells us. That's the bit I was getting stuck on, I was putting myself in Albert's shoes forgetting that he knew the month.

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If you like stories with knights who always tell the truth and knaves who always lie - try the book - "What is the name of this book?"

 

I've been picking it up doing a few of the hundreds of puzzles it consists of and then leaving it aside for about 2 years now.

 

Plus read this blog post - it's brill!

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Logic used to be taught in schools, now they don't even teach spelling, progress...

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Declan, If it was June, Albert wouldn't be able to say "I know Bernard doesn't know". Do you get why?

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I'm crap at these sorts of things, but I'd assume the day would have to be unique, so either

 

May 19

or

June 18

 

ETA - or perhaps the complete opposite.

Edited by The Old Git

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Unless I'm being daft...

 

 

 

Albert knows the month, and he declares that Bernard can't know the birthday. The only way Bernard COULD have known the birthday from just the day alone was if it was May 19th or June 18th.

Therefore it's not May or June.

 

After being told it's not May or June, Bernard knows what the birthday is. So you're looking for a number that occurs in May or June, and also in one of the remaining months, but not BOTH of the remaining months.

 

Which makes it August 17th, right?

 

EDIT: Balls, same logic allows for July 16th

... and August 15th

 

EDIT2: Too early in the day apparently. I missed the bit about Albert knowing the answer once Bernard knows. Albert realises it must be July 16th, August 15th or August 17th. Since he knows the month, it has to be July 16th.

 

Edited by HeliX
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These things are best solved, if you can't just 'see' the answer, with a grid. Draw a grid with numbers across the top, and months down the side, then put a cross in boxes that correspond to possible dates. Then cross out rows and columns according to the instructions.

 

The first instruction is 'A knows that B doesn't know'. A knows therefore that B hasn't been given a unique number (either 18 or 19, because then B would know) so A, given he knows the month, has basically announced that the month is not either May or June. So on your grid cross out those rows.

 

B, on working this out, then knows the month is either July or August. He announces he now knows the date, which means he hasn't been given the number 14, so this column can be crossed off your grid.

 

As A now announces he also knows the date, there's only one possibility, as you can cross out the row with 2 numbers left.

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