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Someone posted this in my bw qq(chat) group just now and I thought people on TL would like this. Original names are replaced with English ones.
John and Mike are both pupils of Mr.Stevenson, Mr.Stevenson's birthay is on M/N, M = Month, N = Date. Mr. Stevenson told John "M" and Mike "N". John and Mike both know Mr.Stevenson's birthday is one of the following 10 dates.
3/4 3/5 3/8
6/4 6/7
9/1 9/5
12/1 12/2 12/8
John says: "If I don't know the date, then Mike can't either"
Mike says: "I didn't know it at first, but now I know it"
John says: "Now I know it too."
From the above conversation, figure out what Mr.Stevenson's birthday is.
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Aotearoa39261 Posts
haha my friend gave this to me in stats class was wtf at first but yea
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either 9/1 or 12/1 my guess is 12/1
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+ Show Spoiler + i dont have any logic, im bad for riddles, but mike said 'i didnt know it at FIRST' so he might be telling him a clue that its on january
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argh.. ignore what i said earlier lol
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Its more logic than math imo..
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The month can't be 12 or 6. The guy starts off by saying his friend can't know the date. Both december and june have days exclusive to them and there is no way for John to know that Mike didn't get an insta-win. My guess is Mike's number is a 5. So either 3/5 or 9/5.
btw, I don't understand why it starts "If I don't know the date.." How on earth could he know the date? All he was given was the month of the year and every single month has more than one day that it could be.. There's no if.
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On January 22 2008 23:02 dybydx wrote:means knowing day or the month number alone is not sufficient to determine which 1 is correct thus it can not be 6/7 and can not be 12/2
How can John know this ??? He has only the month number. There is no way to reach that conclusion.
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On January 22 2008 23:04 BlackJack wrote: The month can't be 12 or 6. The guy starts off by saying his friend can't know the date. Both december and june have days exclusive to them and there is no way for John to know that Mike didn't get an insta-win. My guess is Mike's number is a 5. So either 3/5 or 9/5.
btw, I don't understand why it starts "If I don't know the date.." How on earth could he know the date? All he was given was the month of the year and every single month has more than one day that it could be.. There's no if. + Show Spoiler +ah it´s 9/1. misread something
1. statement: month 3 and 9 are left 2. statement: days 1, 4 and 8 are left 3. statement: day 1 is left => 9/1
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+ Show Spoiler +John says: "If I don't know the date, then Mike can't either"
Means that it cant be either in the month 6 since thn Mike could have known the date 6/7. It cant be any in the month 12 either for the same reason.
Mike says: "I didn't know it at first, but now I know it"
Means it is one of the number which are single days 3/4 3/8 and 9/1
John says: "Now I know it too."
means it is 9/1
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maybe we should all use spoiler tags
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On January 22 2008 23:19 dybydx wrote:means knowing day or the month number alone is not sufficient to determine which 1 is correct thus it can not be 6/7 and can not be 12/2 Mike realizes that if John knows day number is insufficent, it means it can not be 6/X or 12/X Now Mike knows the number. John realizes his statement allow Mike to deduce the month number. This means the day number must b 8, since 8 is in both 3/X and 12/X ANSWER: 3/8
Haha you are falling at the finish..
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Yeah I didnt understand why it couldnt be 12\8
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John says: "If I don't know the date, then Mike can't either" means knowing day or the month number alone is not sufficient to determine which 1 is correct
thus it can not be 6/7 and can not be 12/2. Thus John knows it can not be 6/X or 12/X
Mike says: "I didn't know it before, but now I know it" Mike realizes that it can only be 3/X or 9/X Now Mike knows the number.
John says: "Now I know it too." John realizes his statement allow Mike get the month, thus it can not be 3/5 or 9/5 This leaves 3/4, 3/8 and 9/1 Now John has the answer. Because the number he has is 9
ANSWER: 9/1
Meander got it first. GJ
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how can you conclude that if 12/2 is impossible, 12/1 and 12/8 are impossibe too?
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On January 22 2008 23:31 dybydx wrote:means knowing day or the month number alone is not sufficient to determine which 1 is correct thus it can not be 6/7 and can not be 12/2. Thus John knows it can not be 6/X or 12/X Mike realizes that it can only be 3/X or 9/X Now Mike knows the number. John realizes his statement allow Mike get the month, thus it can not be 3/5 or 9/5 This leaves 3/4, 3/8 and 9/1 Now John has the answer. Because the number he has is 9 ANSWER: 9/1 Meander got it first. GJ
Maybe it is because of my English, but I don't get it at all. If you can explain the first statement a little bit more, that would help me understand the whole thing a lot.
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Statement 1: John has the month number, and using that number alone, he knows Mike will not be able to determine the date. Thus John knows the date is not 6/7 or 12/2. He knows this because the month number he got is not 6 and not 12.
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