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Puzzles

For discussions related to education and educational institutions.
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Alan H
Posts: 22737
Joined: July 3rd, 2007, 10:26 pm

Puzzles

#1 Postby Alan H » April 13th, 2015, 12:59 pm

Simon Singh just Tweeted this. Apparently it's a problem for ten-year-olds in Singapore:

2015-04-13_12h57_09.png
2015-04-13_12h57_09.png (256.16 KiB) Viewed 1360 times


Simon reckons it's not trivial...
Alan Henness

There are three fundamental questions for anyone advocating Brexit:

1. What, precisely, are the significant and tangible benefits of leaving the EU?
2. What damage to the UK and its citizens is an acceptable price to pay for those benefits?
3. Which ruling of the ECJ is most persuasive of the need to leave its jurisdiction?

Maria Mac
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Joined: July 3rd, 2007, 10:34 pm

Re: Puzzles

#2 Postby Maria Mac » April 13th, 2015, 2:09 pm

I don't think it's clear from the text that Cheryl told Albert just the month and Bernard just the day of her birthday. It's impossible unless that is understood.

Maria Mac
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Re: Puzzles

#3 Postby Maria Mac » April 13th, 2015, 2:21 pm

The answer is
Spoiler:
July 16
reached by process of elimination. Tough one.

Edited to add: SPOILERS BELOW. Read no further if you want to work out by yourself.

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Tetenterre
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Re: Puzzles

#4 Postby Tetenterre » April 13th, 2015, 2:30 pm

Nice bit of elimination logic. Tough for 10-yr olds, though!


Edit:
Athena wrote:I don't think it's clear from the text that Cheryl told Albert just the month and Bernard just the day of her birthday. It's impossible unless that is understood.
I took that to be implied by the "respectively". :wink:
Steve

Quantum Theory: The branch of science with which people who know absolutely sod all about quantum theory can explain anything.

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Alan H
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Re: Puzzles

#5 Postby Alan H » April 13th, 2015, 2:50 pm

Tetenterre wrote:Nice bit of elimination logic. Tough for 10-yr olds, though!
Apparently, it was 14/15 year-olds.
Alan Henness

There are three fundamental questions for anyone advocating Brexit:

1. What, precisely, are the significant and tangible benefits of leaving the EU?
2. What damage to the UK and its citizens is an acceptable price to pay for those benefits?
3. Which ruling of the ECJ is most persuasive of the need to leave its jurisdiction?

Maria Mac
Site Admin
Posts: 8954
Joined: July 3rd, 2007, 10:34 pm

Re: Puzzles

#6 Postby Maria Mac » April 13th, 2015, 10:01 pm

Tetenterre wrote:
I took that to be implied by the "respectively". :wink:

Well good for you! :cross:

I just read and re-read that sentence thinking,"what does it mean by 'respectively'?" :redface:

:laughter:

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Altfish
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Re: Puzzles

#7 Postby Altfish » April 13th, 2015, 10:20 pm

So, the logic of this is....

Albert's statement tells us that his month is either July or August because he wouldn't have been able to make the statement about Bernard's knowledge if it had been May or June because both have unique dates.

Then because Bernard is looking at the 16; he has used the same logic as Albert to eliminate May and June, leaving only July

Very good, I like that :smile:

Maria Mac
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Re: Puzzles

#8 Postby Maria Mac » April 13th, 2015, 10:39 pm

Brilliantly concise, Altfish. I had to write each step of my thought process to work it out. Here it is:

Albert is told the month, Bernard is told the day

If Bernard is told:

14, it could be 14 July or 14 August
15, it could be 15 May or 15 August
16, it could be 16 May or 16 July
17, it could be 17 June or 17 August
18 it could only 18 June
19, it could only be 19 May

Albert realises that if Bernard has been told either 18 or 19, he will know the birthday because there is only one option for each.

But Albert says he knows that Bernard doesn't know the correct date. How can Albert be so sure? It's because Albert has been told the birthday is either July or August - not May or June, so we can eliminate May and June.

Once Albert has said he knows that Bernard doesn't know the correct date, this tells Bernard that Albert has been told it's either July or August, not May or June.

Bernard then says he now knows when the birthday is whereupon Albert says he also now knows when it is.

We are left with 14 July or 16 July or 14 August, or 15 August or 17 August.

We can eliminate 14 July and 14 August because it would be impossible for Bernard to have worked out which of these it is. We can eliminate the 15 and 17 August because it would be similarly impossible for Albert to work out which it is. But if Bernard has been told the day is 16, then it can only be 16 July. And if Albert has been told July then it can only be - the answer 16 July.

Here are some other explanations. I think I'd find the first one quite hard to follow if I hadn't already done it, the second one is OK. http://www.independent.co.uk/news/world ... 73090.html

http://www.theguardian.com/science/alex ... hs-problem

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Tetenterre
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Re: Puzzles

#9 Postby Tetenterre » April 14th, 2015, 8:50 am

Athena wrote:Well good for you! :cross:

<meep>
Sorry, Athena....
</meep>
:exit:
Steve

Quantum Theory: The branch of science with which people who know absolutely sod all about quantum theory can explain anything.

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animist
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Joined: July 30th, 2010, 11:36 pm

Re: Puzzles

#10 Postby animist » April 14th, 2015, 9:03 am

Tetenterre wrote:
Athena wrote:Well good for you! :cross:

<meep>
Sorry, Athena....
</meep>
:exit:

that is actually quite funny. The one thing I did get about the puzzle was this aspect of it. I determined not to view the spoiler, but the later posts told me (eventually) both the answer and how those poor young Singaporeans would have worked it out, if any of them did so :wink:

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animist
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Re: Puzzles

#11 Postby animist » April 14th, 2015, 11:04 am

animist wrote:
Tetenterre wrote:
Athena wrote:Well good for you! :cross:

<meep>
Sorry, Athena....
</meep>
:exit:

that is actually quite funny. The one thing I did get about the puzzle was this aspect of it. I determined not to view the spoiler, but the later posts told me (eventually) both the answer and how those poor young Singaporeans would have worked it out, if any of them did so :wink:
Actually, they may have been only 14 or 15 BUT they were maths wizzes in in a mathematical Olympiad, so no need for anyone to feel they should have got this!


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