On Friday I posted this puzzle…..

Imagine arranging 6 glasses in a row and filling three of them with water like this….

Every time you pick up a glass it counts as a move.  What is the smallest number of moves that needs to be made in order to leave the glasses alternating full and empty?

If you have not tried to solve it, have a go now.  For everyone else the answer is after the break.

One move.  You pick up the glass that is third from the left, pour its contents into the glass on the far right, and put it back.  Did you solve it?  Any other solutions?



    1. Wait a minute! The question is flawed if all these answers are correct. It states “leave the glasses alternating full and empty?” this means full first and then empty and so on…. this means that the first glass is to be full the second glass empty the third glass full etc… Can this be solved in one move? No.

  1. First answer was two, then I figured out about pouring and got this one. And then, I figured out that you could just use a few physics tricks to slowly but surely transfer the water from one glass to the other without picking it up. For instance, dip a straw into the water, cover the top end with a finger, then pick it up and move it to the other glass, letting air pressure hold in the water, and release your finger. Repeat until the glass is virtually empty, then apply mouth the straw to drink up the remainder.

  2. I used 0 moves. Use a straw to suck up the water in the cup third from the left and drop it in the glass on the far right. Do it over and over again, until the glass is entirely full. No need to touch any glasses.

  3. got the ‘right’ answer before reaching the end of the question: it helps when you know you have to think laterally! after some time I came up with a zero move answer. by using a very log bendy straw you could siphon the contents of the third glass into the sixth.

    1. Gravity demands the empty glass to be lower than the full glass in orther to let the bend straw-method work. Otherwise you will end up with two half-full glasses.

      A small pump would work though.

    2. No, you may transfer all the water by lowering the *very long bendy straw* at first beneath the table. After sucking the air out of it, all water will get into it (again: very long straw). Keep sure to close the lower end of the straw by bending it. After all water is in the straw bring it back above the table over the very right glass and release the water into it.

    3. You might as well get another glass and the straw. That would make more sense then a very, very long straw.

  4. I won’t get too cocky because I know the next one will probably be a stinker that I won’t get close to, but this one took me a couple of seconds.

  5. There were very few rules so being imaginative in solving this puzzle was easier. Hey – the straw ideas were very clever. Well done to those who thought of it!

  6. Nah – I had the given solution in 2 seconds. But as I am a well trained by the puzzles here, I was looking for more … and came to the following: just shift the glasses on the table and don’t ‚pick them up‘ you will end up with zero moves 😉

    1. Defining a move as ‘picking up a glass’ gives away all the solution. With a correct wording of the problem your alternative solution should be the natural “try”, the real point of the puzzle. But then a move should be defined on the basis of the number of glasses you need to touch, and obviously your solution (shifting the glasses) would require more than one.

    1. This is the real answer. Completely acceptable within the wording of the question – nice one.

  7. It took seconds to come up with the 2 move answer. Then I thought that would not be it.

    About an hour later I suddenly figured the real sollution…

  8. Well

    First time I said 1 move: 3 -> 6
    After that I saw “…alternating full and empty” … so tend to say 2 moves :


  9. That was my first Solution. Then I came up with ZERO moves:
    Take a straw, and suck the water from the glass (third from left) and spit it into the glass on the right.
    The rule was, every time I pick up a glass, is a move. So this leaves 0 moves.

    1. BS question with vague rules… If pouring water out of a glass, or additional tools are allowed, how about if I wait until all the water evaporates, then I drink a bunch of water until my piss is practically pure water, then piss in each alternating cup until they are full? I mean, whats with the extra paraphernalia people are imagining they have access to like straws and pumps? Shouldn’t it be assumed by the nature of the question that you have to leave the contents of the glasses as is? If pouring from one glass to another is allowed, then why the fuck is it such a conundrum?

      Tell me that BS up front next time or don’t bother asking please. And why bother pouring the contents of glass 3 in to 5? Why not just dump 3 and demolish 4 or 5? I don’t have to “pick up” 3 to dump it’s contents, or 4 or 5 to smash them. I can do this in zero moves with out any of your pumps or straws, ya jack wagons!

    2. sorry that reply was meant as a stand alone comment, not a reply to you in particular Patrick.

  10. After some other solutions here is my favorite:
    smasch/destroy two of the full glassed and one of the empty glasses on the right side, with a stone or with something else…
    as the task did not include to maintain the number of glasses..
    would also result in “zero” moves…

  11. Got it.
    BTW, if people want to add extra utensils to do it in zero moves, fine.
    If Richard wants to post puzzles without a million clauses, fine.
    Who honestly cares?
    It doesn’t affect my enjoyment of a simple puzzle.
    I knew what the puzzle meant. Context, subtext, implications, logic.
    Human communication is based on these things.
    The puzzle brightened my Friday morning for approximately 1 minute and 30 seconds. That, I assume, was the intention. Thank you, Richard. :^D

    1. that was pretty much my idea too. It’s also not about solving the puzzle, it’s about getting you to THINK about how to solve the puzzle. Who cares what the ‘right’ answer is if it works?

  12. I was right-Yay.
    I have to make the most of this because it doesn’t always happen- it’s the little things that make you grin!

  13. I guessed one move then thought I’d better check, I started with rioja and 6 glasses as in the diagram. I lifted glass 3 and found ALL the glasses empty! Does it only work with water?

  14. First I got the 2 moves simple solution, then after a few minutes, this one.

    Others include sliding the cups along the table instead.

    Also they could be arrange alternatingly in a perpendicular fashion to the current point of view. So that they would be at difference distances (size would have to be adjusted, but who said the cups are equally big?)

    Nice puzzle.

  15. Zero moves, without using utensils. You don’t need to pick the glasses up to rearrange them. Just slide them around on the surface they’re resting on into whatever arrangement you want.

  16. The puzzle should have been worded passively. A glass being picked up (or touched) is a move, not YOU picking up a glass. Otherwise you could get someone else to do whatever for 0 moves since you did not touch anything. There is bar bet that take advantage of that idea. http://www.free-beer.net/?p=15

  17. Got it in about a second, my year 5 class also solved it in one move and about 5 seconds!! Have to say did spend a while second guessing myself as normally I scratch my head over these for ages 🙂

  18. It’s the solution I got but there is this niggling thought that isn’t that alternating empty and full not alternating full and empty as the problem stated…?

  19. “Every time you pick up a glass it counts as a move.”
    “What is the smallest number of moves that needs to be made in order to leave the glasses alternating full and empty?”
    Sooo, if you install the glasses one by one, you have to do six moves before the beginning of the Friday Puzzle.

    If you start by the left glasses and that you don’t do the four last moves, you “leave the glasses alternating full and empty”.

    It is four less moves than the zero solution.


  20. I got Zero moves, as a move = picking up a glass.

    Along with a few other commentators, above I slid the glasses into the correct positions (much as one would slide cups the ‘which cup is the ball under’ game)

  21. To answer the question that you put I don’t think you gave the right answer. Your question was about the smallest number of moves that need to be made in order to leave the glasses alternating FULL and EMPTY. You solution left them alternating EMPTY and FULL. To do that it takes two moves; pour 2 into 1 and 4 into 5.

  22. I initially came up with the one move solution (pour the contents of G3 into G6), but then thought Richard might be playing games with us, so came up with same “Free Beer” solution as Edward V:

    Every time *YOU* pick up the glass, it counts as a move. So, if you have a friend with you, ask them to perform the one-move solution. As *YOU* haven’t picked up the glass, a literal interpretation of the rules would mean that the task had been completed in zero moves.

  23. I solved it right away. I assumed the solution required that the leftmost glass had to be full, so after I completed Richard’s steps, I simply sat on the opposite side of the table.

  24. Wait a minute!! If all these answers are correct, the question is flawed. The puzzle states “…leave the glasses alternating full and empty?” this means that the first glass is full the second empty the third full etc… This cannot be done in one move..
    Unless like JBABB – you sit on the other side of table. Awesome!!

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