[Discussion] Solve this
- Thread starter Aya San
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Kai NB
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Basically this is what happened.
Albert knows the month
Bernard knows the day
Now Albert said that he doesn't know the birthday, but he knows Bernard doesn't either. Albert knows which month it is. Listen closely to this. If Bernard did know the day, he would be able to figure it out instantly if it was the 18th or 19th. The ONLY way for Bernard to know the Birthday is if there are NO duplicates. However, those options are only in May and June. Because Albert said that Bernard doesn't know, it means the month cannot be May or June.
So now we have July and August only. Bernard then says he knows what the Birthday is. The same principle applies. Bernard knows the Birthday only if there are no duplicates. It can't be the 14th, because if it was, Bernard wouldn't know what to choose. It can only be the 15th, 16th, or 17th. Now Bernard knows the day, so he knows it has to be July 16th.
So now we are back to Albert. Albert already knows what month it is. His choices were basically the 14th of 16th of July. But since he knows that Bernard knows, he knows it has to be a number that is not a duplicate. It wouldn't work with the 14th because Bernard already threw that out. So all that's left is July 16th
July 16th is the *****'s birthday.
Albert knows the month
Bernard knows the day
Now Albert said that he doesn't know the birthday, but he knows Bernard doesn't either. Albert knows which month it is. Listen closely to this. If Bernard did know the day, he would be able to figure it out instantly if it was the 18th or 19th. The ONLY way for Bernard to know the Birthday is if there are NO duplicates. However, those options are only in May and June. Because Albert said that Bernard doesn't know, it means the month cannot be May or June.
So now we have July and August only. Bernard then says he knows what the Birthday is. The same principle applies. Bernard knows the Birthday only if there are no duplicates. It can't be the 14th, because if it was, Bernard wouldn't know what to choose. It can only be the 15th, 16th, or 17th. Now Bernard knows the day, so he knows it has to be July 16th.
So now we are back to Albert. Albert already knows what month it is. His choices were basically the 14th of 16th of July. But since he knows that Bernard knows, he knows it has to be a number that is not a duplicate. It wouldn't work with the 14th because Bernard already threw that out. So all that's left is July 16th
July 16th is the *****'s birthday.
Funky Tiger
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[9:26:02 AM] Aya San:
i've been doing this ever since you sent this on skype, and it is now 10:54 and i got an answer.
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i've been doing this ever since you sent this on skype, and it is now 10:54 and i got an answer.
The Sach
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For the explanation to make sense, write all the date on piece of paper and write what Albert and Bernard know.
Albert knows month: May, June, July, August
Bernard knows date: 14,15,16,17,18,19
Dates: 15 May, 16 May, 19 May, 14 June, 18 June, July 14, July 16, August 14, August 15, August 17.
So I finally got it.Lol
Albert knows month: May, June, July, August
Bernard knows date: 14,15,16,17,18,19
Dates: 15 May, 16 May, 19 May, 14 June, 18 June, July 14, July 16, August 14, August 15, August 17.
Statement 1:
Albert: I don’t know when Cheryl’s birthday is, but I know that Bernard doesn't know too.
Now, since Albert knows only month, first part of statement is redundant(one month has more than one dates).
On the other hand, Bernard knows only date and he doesn't know date and month and hence 18 and 19 which constitute to only May and June will ruled out, since these are the only dates that belong to one month only.
Thinking it other way around, Albert shouldn't have been told May or June for 8 or 19 to occur and hence 18 June and 19 May are ruled out.
Leaving out,
Albert: July, August
Bernard: 14,15,16,17
Dates left:July 14, July 16, August 14, August 15, August 17.
Statement 2:
Bernard: At first I don’t know when Cheryl’s birthday is, but now I know.
At first didn't know the month, but now after listening to Albert, he figured out that month is either July or August.
He knows exact date and based upon date he was able to figure out the month. So the date must be such that it isn't common between both the months and hence the date which is common between July and August is ruled out, which is '14'.
So,
Albert: July, August
Bernard: 15,16,17
Dates left: July 16, August 15, August 17.
Statement 3:
Albert: Then I also know when Cheryl’s birthday is.
Now, Albert deduced that 14 isn't possible from Bernard's above statement.
Also, he knows the month and hence month should be such that, it shouldn't be common between both the dates.
The only month with one date is July and hence answer is July 16, which is the solution.
Just found out that, this is can also be solved using set theory, btw.
Albert: I don’t know when Cheryl’s birthday is, but I know that Bernard doesn't know too.
Now, since Albert knows only month, first part of statement is redundant(one month has more than one dates).
On the other hand, Bernard knows only date and he doesn't know date and month and hence 18 and 19 which constitute to only May and June will ruled out, since these are the only dates that belong to one month only.
Thinking it other way around, Albert shouldn't have been told May or June for 8 or 19 to occur and hence 18 June and 19 May are ruled out.
Leaving out,
Albert: July, August
Bernard: 14,15,16,17
Dates left:July 14, July 16, August 14, August 15, August 17.
Statement 2:
Bernard: At first I don’t know when Cheryl’s birthday is, but now I know.
At first didn't know the month, but now after listening to Albert, he figured out that month is either July or August.
He knows exact date and based upon date he was able to figure out the month. So the date must be such that it isn't common between both the months and hence the date which is common between July and August is ruled out, which is '14'.
So,
Albert: July, August
Bernard: 15,16,17
Dates left: July 16, August 15, August 17.
Statement 3:
Albert: Then I also know when Cheryl’s birthday is.
Now, Albert deduced that 14 isn't possible from Bernard's above statement.
Also, he knows the month and hence month should be such that, it shouldn't be common between both the dates.
The only month with one date is July and hence answer is July 16, which is the solution.
Just found out that, this is can also be solved using set theory, btw.
Venomous Cobra
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-immortal-
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It's simple enough if worded right.
A= Albert
B= Bernard
may 15
may 16
may 19
june 17
june 18
july 14
july 16
august 14
august 15
august 17
may 16
may 19
june 17
june 18
july 14
july 16
august 14
august 15
august 17
july 14
july 16
august 14
august 15
august 17
july 16
august 14
august 15
august 17
july 16
august 15
august 17
august 15
august 17
july 16
Venomous Cobra
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I understood the solution perfectly, but I'm just saying that it ain't "simple". The elimination process Itself was easy but the fact that only the unique number can be the date of her birthday was fairly challenging .
Nice thread btw, this was bit entertaining.
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HashiraMadara SenjUchiha
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It's July 16... I remember having to answer this question in school as part of a prize, eliminating all answers for only logical possibility. Still today, nothing seems logical about it...
I was gonna ask if you googled it, instead I copy and pasted your answer into google. Nice job googling it.
For anyone wanting to know a... more simple way of understanding this that wasn't just copy and pasted by others, it goes like this...
Albert knows the month, meaning he knows it's either May, June, July or August.
Bernard knows the day, meaning he knowing it's either 14, 15, 16, 17, 18 or 19.
Now that we know what they potentially know, it's down to eliminating possibilities. May 19 and June 18 are singles, no other date corresponds to their day of the month, meaning they are possibilities. As for the rest in May and June, they share the same day of the month with other months. Since Bernard knew the day, but not the month, if he knew the day were 18 or 19, that would mean he also knows the month. Since he does not know her birthday, that means it cannot be May 19 or June 18. That's two dates down, 8 to go.
Albert knew Bernard didn't know the exact day of birth, but why? If Cheryl told Albert the months of her birthday were either May or June, then it's possible that the birthday would have been 19 and/or 18. However, since Bernard did not know the birthday, but knew after Albert made the statement, that would mean it cannot be May or June, so it must be July or August. 5 down, 5 to go.
Now we have July and August left. Bernard now knows the exact day of which Cheryl's birthday is. The day 14 pops up twice. Since Bernard now knows the date, that means he knows exact month, meaning he couldn't do a 50/50 guess on July 14 or August 14, eliminating those 2 dates from the pool. Now we have July 16, August 15 and August 17.
With 3 dates left, we now know both parties know the exact dates of which Cheryl's birthday is. If Bernard know the day number, he would know the correct day and month, as only 1 of each number remains. Albert too knows the answer, but how do we know which of the 3 it is? If Albert knows the day and month, then if Cheryl told Albert her birthday was in August, he would have a 50/50 chance of choosing the right day, August 15 or August 17. Since he doesn't know which is correct, but statement says he does know, August cannot be a remaining month.
That means, of the 10 dates given, the only possible date left is July 16th.
Albert knows the month, meaning he knows it's either May, June, July or August.
Bernard knows the day, meaning he knowing it's either 14, 15, 16, 17, 18 or 19.
Now that we know what they potentially know, it's down to eliminating possibilities. May 19 and June 18 are singles, no other date corresponds to their day of the month, meaning they are possibilities. As for the rest in May and June, they share the same day of the month with other months. Since Bernard knew the day, but not the month, if he knew the day were 18 or 19, that would mean he also knows the month. Since he does not know her birthday, that means it cannot be May 19 or June 18. That's two dates down, 8 to go.
Albert knew Bernard didn't know the exact day of birth, but why? If Cheryl told Albert the months of her birthday were either May or June, then it's possible that the birthday would have been 19 and/or 18. However, since Bernard did not know the birthday, but knew after Albert made the statement, that would mean it cannot be May or June, so it must be July or August. 5 down, 5 to go.
Now we have July and August left. Bernard now knows the exact day of which Cheryl's birthday is. The day 14 pops up twice. Since Bernard now knows the date, that means he knows exact month, meaning he couldn't do a 50/50 guess on July 14 or August 14, eliminating those 2 dates from the pool. Now we have July 16, August 15 and August 17.
With 3 dates left, we now know both parties know the exact dates of which Cheryl's birthday is. If Bernard know the day number, he would know the correct day and month, as only 1 of each number remains. Albert too knows the answer, but how do we know which of the 3 it is? If Albert knows the day and month, then if Cheryl told Albert her birthday was in August, he would have a 50/50 chance of choosing the right day, August 15 or August 17. Since he doesn't know which is correct, but statement says he does know, August cannot be a remaining month.
That means, of the 10 dates given, the only possible date left is July 16th.
Alice in Noodleland
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Awkward Linguist
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