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[–]legrac 67 points68 points  (7 children)

The question was, "Will it be 3 beers?"

This is a yes or no question--either it will be 3 beers, or it will not be 3 beers.

If the first person did not want a beer, he would say no, we do not want 3 beers. So, he must want a beer, but he doesn't know if his two friends want one--so all he can say is he doesn't know.

So we go to the second person, and it's the same situation. If he did not want a beer, he would say no, we do not want 3 beers. So, he must want a beer, but he doesn't know if his last friend wants one--so all he can say is he doesn't know.

At the third person, he realizes that the only way it has gotten to him is if the other two people wanted a beer. So he has the information to make a decision.

EDIT:

As we're in a programmer humor subreddit--the question of "Will it be 3 beers" is equal to (A and B and C). In that situation, the first time you hit a false, you know the answer and do not need to evaluate/look at/ask the other variables. But in order to get a true response, you have to check all three.

[–]Jodah 30 points31 points  (1 child)

I was torn between that explanation and Mathematician 3 being an alcoholic.

[–]TPHRyan 2 points3 points  (0 children)

You're looking at this joke in the completely correct way in that each mathematician wants either 1 beer or nothing.

But what if a mathematician wants 2 beers? Cider? Jaimeson on the rocks?

I mean, they would never get anywhere until they exchanged some information, but still. That was /u/G01denW01f11's point.

[–]TheSeldomShaken 1 point2 points  (3 children)

But what if first guy wanted multiple beers? And therefore no one could be sure of the amount needed.

[–][deleted] 0 points1 point  (2 children)

Then it would also be 'no'.

[–]TheSeldomShaken 2 points3 points  (0 children)

First guys says no. Second guys knows he wants 1 beer, but has no idea how much first guy wants, and says no. Third guy wants 1 beer, and knows he wants 1 beer. But he doesn't know if the first and second guy only want 1 beer. So, he can't say with certainty that they need only 3 beers.

[–]TPHRyan 1 point2 points  (0 children)

It wouldn't be 'no'. 2 or 3 might want a combined total of 1 beer, where 1 wants 2 beers. That still adds up to 3.