Maths|Logic - (1 Viewer)

AnthonyGerrard

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Oh, for the love of God.

I had no intention of contributing here ever again, but this is driving me insane, watching you people flounder about.

The birthday is July 16.

  • A knows for a fact that B cannot know the exact birthday. As he knows the month but not the day, that means the month is one without a unique day listed. This eliminates both May (the 19th) and June (the 18th).
  • B realizes the above. Since he knows the day and now is aware that it must be either July or August, this tells him the exact birthday. This means that the day CANNOT be the 14th, or he would not have figured that out.
  • A now knows the above. Since he knows the month, and now knows that it cannot be the 14th, he also knows the exact date. If the month were August, he would not have been able to determine the exact day, so this eliminates August, which had both the 15th and the 17th remaining.
  • The only date meeting the above criteria (Not in May, June, or August and not the 14th) is July 16, making that the birthday.

The man has it - well done! and well explained too.

You've been lurking!
 

AnthonyGerrard

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A knows the month and B knows the day
Since B doesn't know we can obviously rule out the single days May 19 and June 18
But since A knows that B doesn't know he can also rule those out, which since he still doesn't know that also rules out June 17, which is where I answered too quickly first time.
Onto second sentence
With A still not knowing and thus ruling out June 17 the only possible solution is August 17 as it is the only unambiguous day.

That's my 2p worth. Hoped I explained my logic ok.

Brian

I'll read it over the weekend - Frothy has it right.
 

Frothingslosh

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The man has it - well done! and well explained too.

You've been lurking!

I have. I'm pissed, not stupid. This website is too useful a resource to just throw away, and I've never been one to cut off my nose to spite my face.
 

AnthonyGerrard

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I have. I'm pissed, not stupid. This website is too useful a resource to just throw away, and I've never been one to cut off my nose to spite my face.



I'm pissed too - which is why I'm not going through Brian's workings now. I think we use the phrase differently however!

Welcome back!
 

AnthonyGerrard

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A knows the month and B knows the day
Since B doesn't know we can obviously rule out the single days May 19 and June 18
Brian

Yes - but as frothy says you can go further than this - cos A knows that B definitely doesn't know initially - it can't be either may or june. Otherwise there is the possibility that B does know.


ie we know A has July or August.
 

Brianwarnock

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I'll read it over the weekend - Frothy has it right.

Does he have it right because it agrees with you or do you have the result and explanation from elsewhere?

I know I'm getting old and maybe a bit slow but I cannot fathom Froth's first sentence, it does not seem logical to me but a step too far.

Brian
 

Brianwarnock

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Yes - but as frothy says you can go further than this - cos A knows that B definitely doesn't know initially - it can't be either may or june. Otherwise there is the possibility that B does know.


ie we know A has July or August.

As I see it the fact that he does not know rules out two days not the whole months

Brian
 

Frothingslosh

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Frothingslosh might have cheated ;)

Or Frothingslosh might have spent 10-15 minutes figuring it out on his own a couple months ago, back when the Singapore Problem first hit the news, because one of his hobbies might be solving logic puzzles.
 

vbaInet

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Or Frothingslosh might have spent 10-15 minutes figuring it out on his own a couple months ago, back when the Singapore Problem first hit the news, because one of his hobbies might be solving logic puzzles.
May well be :eek:
 

BlueIshDan

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As I see it the fact that he does not know rules out two days not the whole months

Brian

If A right off the bat says that they know that B doesn't know at first glance. A must have seen the distinct days within the two months, knowing that they would be the only way B would instantly know the birth date. The only way he would know that they weren't is if the month he had was not one of the two.
 

Brianwarnock

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Hi
Coming home late last night refreshed by a bottle of plonk and no longer distracted by the Giro I switched on my iPad which had the problem still showing on it.
I quickly realised two things
1 that I had been a right plonker in concentrating on the day and forgetting A's knowledge of the month
2 that my grotty eyesight had read August 15 as august 16 which allowed me to get a solution.

Lesson learned
At my age I can't multitask

Cheers to all and thanks to those who tried to help.

Brian
 
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Brianwarnock

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Frothy is there a site which has these logic puzzles, my brain could do with a workout.

Brian
 

AnthonyGerrard

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Just had a go. 296 seconds slow. On an easy small grid. I'll take that for my first go.
 

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