There were 4 kids; 3 brothers and a friend. They all went into a local restaurant and ordered some water. The friend bought the same water the brothers had, but paid more. Assume they all drank bottled water, drank at the same time, drank the same amount, and only drank the water they paid for. If nothing happened to the water after, why is it that only one bottle is empty?

Note from the Author:

I did make this up, it may have some flaws, but I did use this a few times to see if it worked first.

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    $\begingroup$ You may want to add as a fact that everybody drank only the water they paid for. Otherwise you can easily have 4 bottles (same or different size, form, whatever ... doesn't matter) and everyone drank 1/4 of one bottle (split into 4 glasses so they can drink at the same time) which would make this very boring .... $\endgroup$ – print x div 0 Aug 8 '16 at 9:57


The brothers bought 1 bottle for the 3 and the friend 1 for himself. He paid more because he didn't share it. And the brothers could drank at the same time with glasses, because of that, they drank 1/3 each (even the friend ) and have only 1 empty bottle.

  • $\begingroup$ If I read it right they drank 1/4 each right? Including the friend. $\endgroup$ – Jason_ Aug 8 '16 at 6:54
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    $\begingroup$ no. the 3 brothers, 1/3 of their bottle, so the bottle remains empty. the friend 1/3 of his bottle so still 2/3 remaining $\endgroup$ – lois6b Aug 8 '16 at 6:55
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    $\begingroup$ Ooh, well you got it right, slightly different, but nice $\endgroup$ – Jason_ Aug 8 '16 at 6:59

The friend bought 1 bottle, and that is the only bottle they bought. Everyone drank from this bottle (since he bought the same water the brothers had, it could not have been otherwise!), the same amount. The bottle has been paid by the friend, which is more than zero paid by the brothers.

  • $\begingroup$ This was my first thought as well. $\endgroup$ – Eborbob Aug 8 '16 at 12:11

This answer is probably incorrect but

the bottles might have been different size. They bought the same water, i.e. the same brand of water but the friend bought say 1l bottle (and he paid more) and the brothers bought a small one (say 0.5l). So all of them had the same amount of water (0.5/3) and the small bottle was empty in the end but the big one still has water in it.

Ah, somebody was quicker then me by a few seconds.

  • $\begingroup$ Very specific I like it $\endgroup$ – Jason_ Aug 8 '16 at 7:00

Another solution:

The friend ordered high quality bottled water. The brothers ordered tap water. He paid more, there was only his bottle. The water was the same, well, because the bottled water has been produced using the same city water source (as is indeed often the case), or perhaps even refilled at the restaurant.



The friend ordered 1Ltr bottle while the others ordered 500ml bottle. Both are of same company, hence same water. But of different quantity. That's why the friend paid extra.


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