Please do NOT post your answers, but do say if you think you have solved the puzzles and how long it took. Solution on Monday.

John weights much more than 20 stone.  He goes to the shops to buy some scales, but the scales there only go up to 20 stone.  However, he comes up with a way of accurately weighing himself every day using the scales.  What was his plan?

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.


  1. How much is “much more”? Up to 40 stones would be easy. Up to 80 kind of quirky. Above 80 I don’t have a solution.

    1. I think I’ve got the same solution as you. Though I think it would actually be quite a bit trickier in practice than it appears in theory.

      Alternatively, there’s always the method my brother used to weigh his luggage when he didn’t have any scales at all.

  2. Several solutions leap to mind but I guess he’s not planning to disembowel himself or waste the dwindling volumes of helium available so I think he’s going to pick the easy method.

  3. As long as he doesn’t weigh more than 40 stone (at which point he’d probably have problems getting to the shops, so would have to order the scales online!), I have a potential solution which is easy to implement.

  4. I have two solutions, one will work even if he is well over 40 stones, but I guess this is unlikely as he would never have made it to the shops in the first place.

    1. Golf clap. Haven’t heard of that disease before. Do you get that by swinging your wedge about in a bunker?

  5. No problem. Just a few more supplies to get–a good friend with a strong stomach and an open calendar and some heavy-duty trash bags.

  6. Over here weight is measured in “pounds.” (And to be even MORE convoluted, it’s abbreviated as Lbs.) I guess we’re worth our weight in British currency.

  7. Beyond the stones, I’m thrown by all this plural ‘shops’ and ‘scales’ litany of Brittany. I’m going to drive to the store, take the elevator up, buy a scale, and bring it home in the trunk of my car. (If they have one that can handle my stones, that is!) 😉

  8. there are many possible answers to this.

    one is the use the archimedes principle. weigh himself in a bath of water and then subtract the weight of the water. this is easier in metric as one kilo is the same as a liter.

    or he could do the obvious and weigh himself twice.

    1. for a clue…..imagine the degenerate case where he has a scale that can only weight zero stones (or zero pounds or zero kilogrammes. in this case the conversion is easy, not like with Temperature).

      from the soln you have there now imagine he can weight to to twice his weight (not half) on a single scales purchased from the shops.

      now what is the general case? (perhaps a step is to also imagine he weights zero).

  9. Found a solution where John could weigh theoretically any number of stones, let’s say 1000 stones, but this would involve A LOT of scales and I am not sure if this would statically work.

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