It’s the Friday Puzzle!


Here is the puzzle.  As ever, please do NOT post your answers, but do say if you think you have solved the puzzle and how long it took. Solution on Monday.

Given a sack of sugar, an unbalanced scale, and two 5-pound weights, measure exactly 10 pounds of sugar.

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


36 comments on “It’s the Friday Puzzle!

  1. Ken says:

    Think I have it as long as there’s more than 10lbs of Sudra in the sack ! took a minute to double check

  2. spacetiger says:

    Yeah. Few seconds. I like it!

  3. Gib says:

    Can we assume the scale is unbalanced by a difference on each side of less than 5 pounds?
    Then it took me 5 seconds, and I can do it with one weight.

    If the unbalance is between 5 pounds and 10 pounds, then I’d need both weights and some extra sugar. Or, a single weight and a lightweight bag or box.

    If the unbalance is greater than 10 pounds, then I’d need both weights and a lightweight bag or box.

  4. Simon Taylor says:

    Same as Gib.

  5. The Masked Twit says:

    Immediate, if I interpet the meaning of “an unbalanced scale” as a scale that is not innaccurate, but just a scale that does not have each dish at the same height when there is nothing on either of them.

  6. Angela says:

    Sometimes I wonder if I can be right given that they are so obvious.

    Sometimes I’m late for work. Today is the former.

  7. Klaas De Smedt says:

    Here also same as Gib,
    it is possible with one weight of 5 pound

  8. Tom says:

    Usually rubbish at this kind of puzzle, but cracked this pretty quickly. Yay for me.

  9. Julie says:

    I’m ok with this as long as there is somewhere to put the sugar I’m not using. I need another sack.

  10. -M- says:

    Got a sollution (maybe there are more possible). But if the imbalance is bigger than the total weight of the bag of sugar and the weights, it won’t work.

  11. John says:

    It seems easy enough.

  12. Simply pour some of the sugar into some water, and you will have a solution.

  13. Eddie says:

    This seems so simple I’m not even going to bother commenting.

  14. Another spectacularly easy one. Disappointing.

  15. ivan says:

    As is clear from several replies, the difficult bit is to know what properties some “unbalanced scales” should be expected to have, as there are several possible faults that could lead scales to be unbalanced. I suspect that the specific property that Richard has in mind is that the scales can be brought back into balance by the addition of a small weight to one side of the scales, and having got them into balance, addition of equal weights to each side will keep them in balance. We do, of course, have the materials with which to verify that these properties apply.

    • mittfh says:

      That’s the definition of “unbalanced” I thought of. I assumed the imbalance is relatively small and either (a) there’s a supply of spare sacks / bags or (b) the containers on which you place items to weigh are either dishes or have a rim, arriving at a resolution within a couple of seconds (I won’t say ‘arrived at a solution’, as the obvious way to make a solution would require liquid [as Paul indicates above], which doesn’t appear to be present…)

  16. ivan says:

    As an Englishman, I would say that it is scales, not scale, but research leads me to discover that Americans say scale.

  17. Andrew says:

    What if the scales are unbalanced by the arms being different lengths?

  18. Try my puzzle too
    Find a relationship between the input and the output

    The output generates a number based on the string

  19. Indy says:

    got it in 10s!

  20. ctj says:

    it really depends on how many kilograms of sugar i can buy for 10 pounds.

  21. Anonymous says:

    Easy one again :). I’m still thinking about other ways though.

  22. Lazy T says:

    These easy puzzles are sweet but how about a good old sour one next week?

  23. Duncan says:

    I think I know what Richard’s answer will be, but I don’t like it – too many assumptions as usual!

  24. One Eyed Jack says:

    Too easy drill sergeant!

  25. Blaadyblah says:

    About fifteen seconds.

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