Friday, July 12, 2013

A Bar Joke and a Bar Puzzle

First, let me start you on a joke.

A man has been coming to the bar weekly and ordering four small glasses of Scotch. The bartender offered him to take two large glasses instead of four small as it would come cheaper, but the man explained that they are four brothers living far apart from each other. Last time they met they decided that whenever each of them drinks, he should order four glasses to celebrate their brotherhood and imagine them all drinking together.
One day the man came to the bar and ordered three glasses. The bartender started on his condolence assuming that one of the brothers has passed away, but  the man quickly rebutted that everyone is alive only he has recently been at his annual checkup and the doctor told him to stop drinking.

Now, to the puzzle that our fan Ilya spotted somewhere on Facebook (or at the bar?) and thought you would like:

Three very logical people walk into a bar. The bartender asks "Do you all want a drink?"
The first person says "I don't know."
The second person says "I don't know."
The third person says "Yes!"

Question is, what explains such strange answers by these logical people, and why do they actually make perfect sense?
Your thoughts and suggestions are accepted any time until midnight Eastern Time on Sunday, on our Family Puzzle Marathon.

Image by marsmet511 used under CCL.


20 comments:

Anonymous said...

The first 2 people would say 'no' if they didn't want a drink, because then they would be sure that not all 3 wanted one. So they both indicate that they do want a drink. The 3rd person, hearing the first 2, and wanting a drink, now knows for sure that all 3 want a drink, and so her/his answer is "yes."

Tom said...

The puzzle assumes none of the three are uncertain about their own choice y/n; they are only uncertain about the wishes of the others.

If the first person did not wish a drink, #1 would have said NO (we would not all like a drink). #1 did not say NO, therefore WOULD like a drink.

Same with #2, could have said No but did not.

#3 realizes the uncertainty of #1 and #2 arose from their not knowing his/her wishes, and also #3 would like a drink. Yes, we would all like a drink.

Larry Krakauer said...

Good one!

Here's an old "B.C." cartoon by Johnny Hart:

Caveman 1: "Are you a member of the Liar's Club?"

Caveman 2: "Yes"

Caveman 1: "Hey! That's not bad! How would you like to join up?"

anne-marie said...

One explanation is that the first person could not answer for the two others so this person answers :"I don't know".
Because the first did not know, the second could not answer for the third so this second person answered: I don't know and like I don't know is not a "no" the third decided for all of them!

Thad said...

The key is that the bartender asked if they all wanted a drink. The first man must have wanted one, otherwise, he would have known that not everyone wanted one and he would have said so. Since he didnt know if the other two wanted drinks or not, he replied with, "I don't know". Similarly, the second man must have wanted a drink or otherwise he would have told the bartender that not everybody wanted a drink. But the third man knew that each of the first two must have wanted drinks, so he was able to tell the bartender that, yes, they all wanted drinks!

Aunnesha Bhowmick said...

The Bartender asks if they ALL want to have a drink. The first person says I don't know because he does not know what everyone else's choice is. The second person say I don't know because he is not sure if ALL of them want to have a drink. The last person says yes because they all want to have a drink and he knows so because the first two people would of said no if they did not want to.

TyYann said...

The reason is the 3 persons don't know what the others want. So they can't answer "Yes" to "Do you *ALL* want a drink". They can answer "No", if they don't want a drink themselves, or "I don't know" if they want one.
Except for the third person, who heard the 2 others saying "I don't know", meaning they want a drink. Wanting a drink himself, he answers Yes.

Lynnet said...

The key is that they are very logical.
The first person doesn't know if the other two want drinks, but knows that he wants a drink, so he says that he doesn't know.
The second person has the same issue, not knowing whether the third person wants a drink. However, the second person does know that the first person wants a drink.
The third person wants a drink, and now knows that the other two also want drinks, so he says yes.

Jerome said...

Neat Puzzle Ilya

Short answer: they all want a drink.

The catch to this one is looking at the first two answers. Those two undoubtedly do want a drink (otherwise their answer would have been "no").

Just to be thorough, the first person does not know what the other two want to do. He wants a drink, but is uncertain about his friends.

The second person also wants a drink (he did not say no), and he recognizes the first person's uncertainty and correctly concludes that he wants a drink, but does not know what the third person is thinking.

The third person, not hearing a no from the other 2, concludes that they both want a drink and he does as well, so he answers yes. His yes means they all want a drink.

Dennis (of Dennis and Katrina) said...

It's boolean logic. The key word in the question is "all", and is what allows us to explain the answers.

The first person, being first, only knows if he/she wants a drink. Logically, if he/she did not, then the answer to the question is "no", because they "all" do not want a drink. Since the first person says "I don't know", we know that they want a drink.

A similar arguement is made for the second person - he/she knows the first person wants a drink, knows if they do, but does not know about the third person. If the second person did not want a drink, again, the answer to "all" would be no; since the second said "I don't know", they want a drink.

The third person wants a drink, and now knows the first do as well, so he/she can answer the question - "yes!"

Dennis

Norma said...

Because the bartender asked them collectively if they all would want a drink and they obviously cannot answer for their friends' preference, only for themselves :).

Maria said...

Great puzzle, Ilya. Thank you for spotting it and sharing with us. You deserve the 3-puzzle points finders fee:) Everyone - check also out Larry's wording of a related cartoon above. A puzzle point for Larry for it.

You all cracked it out and nicely explained in your own words. The key points here are that all three people walking into a bar are "very logical", and that the bartender is not asking each of them whether they want a drink but rather asks "Do you ALL want a drink?"

Puzzle point for everyone who answered. Have a great week.

LOUISA CONNOLLY said...

I don't!! No!!

vinoo cameron said...

If there is any mathematics here it is this perhaps

3

2/3=I do not know ( negative)

1/3 = yes (positive)

2/3+1/3=1, you see two negatives = +1 positive

Hey its a punn on the question!

Rachelle said...

Great!

Anonymous said...

Something similar from the east (or India as you know it), try reasoning this out and not just giving an answer...

The puzzle goes something like this...
There are some sages (highly esoteric, intelligent and spiritual beings) of equally high level of IQ on an island, lets call the number of sages as 'n'. Now these sages have a "guru" who visits them once a year to give/render some pearls of wisdom, our sages listen to him and go back to their respective cottages in the ashram and meditate, these sages of ours are "maunis" or people who have taken an eternal vow of not speaking. These guys just meet up once in the morning, see each other’s face and go back to their meditation.

Anonymous said...

Now, on one visit, the guru tells them that “at least one of you have a fatal communicable disease, visible as a large red spot on forehead, and risk infecting others within a month. So if you have that disease you should disintegrate your bodies by yogic means to avoid an epidemic”. Say the visit was on the first day of the year for convenience sake. The sages are not allowed any mirrors or any other such amenities where they can see a reflection of themselves and determine if they are infected. The only way out for them is to look at each other’s faces when they meet once in the morning and deduce for themselves if they have that dreaded disease.

Anonymous said...

Now the puzzle, these sages meet every morning as usual after the guru leaves. On the seventh day (that is including the day when guru visited them, ‘coz they saw each other in presence of the guru) all the sages go back after the meeting and disintegrate themselves. Now reason out and determine the number of sages.
The problem has a unique solution and is not just a conjecture. If you find ‘n’ then consider yourself almost as intelligent as those sages (sorry, don’t have brownies that I can give out over the net)

PS: Couldn't contain the entire puzzle in one post so had to split it like this (hope it gets published in the same sequence that I have submitted my post)

Jerome said...

One. For sure there must be at least one. He could never see his own red spot and waited for the guru to leave.

Jerome said...

It could be two. Each sees the other's red spot and knows that his therefore has not disappeared. They both will have to shuffle off this mortal coil.

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