Answer to the Friday Puzzle…..

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First, I am delighted that my new magic trick has been launched! It is called The Grid, and allows anyone to look like a mathematical genius. Details here.

On Friday I posted this puzzle:

Imagine that you have the following three bowls:

Bowl A has an 8 liter capacity, and contains 5 liters of water.
Bowl B  has a 5 liter capacity and contains 3 liters of water.
Bowl C has a 3 liter capacity and contains 2 liters of water.

Can you measure exactly 1 liter, pouring only 2 times?

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

1) Pour water from bowl A to bowl C until bowl C is full.  Then there will be 4 litres left in bowl A and 3 litres in bowl C.

2) Pour water from bowl C to bowl B until bowl B is full. Bowl B is now full (with 5 liters) and there is 1 liter left in bowl C.

I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle(UKhere and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.

32 comments on “Answer to the Friday Puzzle…..

  1. Bob O'H says:

    Oh, that’s what bowl B was for. I just poured the spare water down the drain.

    • Alex says:

      What spare water? B is required to get the 1 litre measurement in the answer.

    • Dharmaruci says:

      i think bob you must have done four pourings. a into c. c into drain, b into drain, a into c.

      leaves one L in a but too many pourings to be close to cigar.

      (cigar would be wet after all that pouring anyaway -:)

  2. EddTheEgg says:

    Alternatively, pour 0.5 litres from bowl C to bowl B, and then pour another 0.5 litres from bowl C to bowl A.

  3. Eddie says:

    I got the answer but now I’m worried about surface tension effects.

  4. Will says:

    Mark the water level in C. Pour C into A, then pour B (3 liters) into C (empty) up to the mark (2 liters). There’s now 1 liter left in B.

    • Ben says:

      Surely just: make a mark of the water level in C. Fill C with the water from any other jug. You can now pour 1 litre anywhere you want from C, you just pour until the water is back at the mark.

  5. Anonymous says:

    Why not just fill B and C from A leaving one litre behind?

  6. Anonymous says:

    oops I forgot you were using liters

  7. Anonymous says:

    A no pour solution…..
    wait for it to evaporate

  8. Scott says:

    The puzzle calls for you to “measure” 1 liter, not get 1 liter of water. So in filling C from A you measure exactly 1 liter. Done. A one-pour solution.

    • mikekoz68 says:

      Well obviously this can’t be the answer because a 1 litre “measure” is contained within the question! Bowl C has a 3L capacity and contains 2L so a 1L measure is right there in the question. There you go – a no pour solution. (these aren’t sol’ns)

  9. -M- says:

    How on earth could I miss this one???? I must have been not well last friday

    I had an alternative solution (after thinking way too long): mark the “2 liter” position on bowl C. Then empty it in bowl A.
    Next, pour water from bowl B to the 2 liter mark in bowl C. Then there is 1 liter left in bowl B…

  10. Julia says:

    yay, I got one! (though only after reading the comments to find out if there is a straight forward answer)

  11. my 11 year old dyslexic som worked this one out in seconds.🙂

  12. Anonymous says:

    my solution was to pour bowls B and C out at the same rate; when C is empty, stop – now you have 1L left in bowl B. Does that count?

    • Alex says:

      One of the lateral solutions I like, and doesn’t rely on extra props (such as marking the bowl). Though this would only work if the bowls had the same sized lip, I think, as you’d need to be sure you pour them at the same rate.

    • -M- says:

      Impossible.

      Pouring speed is dependant on lots of variables, including how much water there is left in the tank.

  13. mikekoz68 says:

    Not a very good puzzle when you know it has to be done in 2 pourings then you can just use trial&error and go thru all the possible combinations mindlessly.

  14. Anders says:

    Leave both B and C in a place with even temperature, wait until C has evaporated, bowl B now contains 1 liter. No pouring and no marking or measuring required. (but a very long time/hot room)

  15. Adam says:

    I did it without bowl B. Fill bowl C with bowl A, leaving 4 litres in bowl A. Empty bowl C then pour the rest of bowl A into. Bowl A will be left with one litre.

  16. ivan says:

    I confess I had asserted on Friday that there had to be a “lateral thinking” solution to this as I did an exhaustive search – there being only 9 possibilities for the first pouring – and couldn’t find a solution. Late on Friday I found the proper solution; my exhaustive search wasn’t as exhaustive as I thought it was. Thanks for a proper problem with a proper solution, though it infuriated me I couldn’t spot it for so long.

  17. Zach says:

    1) Pour all of B into A, leaving B empty and A full
    2) Pour half of C into B – leaving you with not one but two 1-liter containers.

    (This assumes that there are measurement markings on the bowls, though. Is that fair?)

  18. Anonymous says:

    The bowls will not evaporate at the same rate. Different volumes and surface area exposed will effect the evaporation rates

  19. SagiK says:

    Pour all the content from bowl B into bowl A. Then pour half of bowl C into bowl B. Both bowls B and C now have 1 litre of water

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