The candle problem

201204200758 From Futility Closet: "Given a book of matches, a box of thumbtacks, and a candle, how can you fix the candle to the wall so that its wax won’t drip onto the table below?"



    1. I’d actually considered using one match to melt the bottom of the candle to the box but essentially the same solution. However i Kept thinking ‘the candle’s too large to be stable on a box held up by tacks. Plus you’re going to have a problem about hot wax and cardboard.

  1. I thought of the solution immediately, but then spent a while trying to find another solution, as that seemed too simple.  So…I have a  functionally adaptable, but overly suspicious mind?

    1. I know, I mulled it over for several minutes thinking it couldnt be that simple.  Not to be elitist but I would bet readers of Boingboing, wired, make, popular science  etc would have very different results from most.  

          1. And if you don’t light the candle, you don’t have to worry about wax dripping no matter how you set it up.

            I was just going to stick the candle to the wall with hot wax, and leave the box on the table. Free tacks!

  2. Are you kidding? The solution was immediately obvious as soon as I looked at the elements. 
    1. Dump tacks out of the box
    2. Tack box to wall
    3. Light candle and melt a small dollop of wax to hold candle upright in box.
    (or, as Rebecca Hera suggests, tack thru bottom of box into candle.)

  3. the “solution” is bogus.

    it was actually my first thought, but then i realized we are not given enough information about the composition and rigidity of the box, nor the weight of the candle, to say the box will be strong enough to support the candle, if it’s tacked to the wall by one of its sides. certainly the box of tacks in my desk to too flimsy to hold anything larger than a birthday candle, if it were tacked to a wall on one side.

    1.  inverting the box would improve it’s rigidity/ stability, although this may decrease it’s ability to stop wax drippings.

    2. Given a book of matches, a box (sturdy enough to hold a candle, if it were pinned to a wall) containing thumbtacks, and a candle, how can you fix the candle to the wall so that its wax won’t drip onto the table below?

  4. i thought it a trick question, but came up with pinning the box to the wall in which to place said candle before lighting it before checking the jump…honestly

    1.  That was my first thought as well.

      The question was asking how to attach the candle to the wall so wax won’t get on the table…well if the table isn’t against the wall to begin with it doesn’t matter how you attach the candle.

  5. What Rebecca Hera said, except you tear away the end of the box above the flame to avoid a fire. 

  6. Set the candle under the table.  Thumbtack the matchbook to the table leg and just to the side of the candle, right next to the wick.  Thumbtack the box positioned just above the candle and matches.  Carefully twist out one match, leaving it still connected, and deftly light it.  The match should be positioned to ignite three things and eventually a fourth and a fifth, hopefully: first the candle wick.  Then the box.  Then the rest of the book of matches.  Then, eventually, if you have set it up correctly, the table and then the structure containing the table.  Nice work, kid.  This is the stuff true pyros are made of. Don’t forget to run away.

  7. You’re gonna need to use more than one thumbtack to hold that box to the wall. You see, my brain started working out the retention force of a thumbtack and the lever arm of the candle’s weight acting on that retention force. 

    1.  Not to mention the strength of the box itself, with that big candle mass trying to tear it apart and/or bend the flimsy shirtboard.

      Heck, you could build an entire AP physics exam from this one problem.

    2. Which is why I kept trying to think of a better solution since sure it might hold the candle as is, but once you get wax pooling either the cardboard fails due to it being wet, or it fails because the wax has redistributed far enough away from the thumbtacks that they nolonger can hold the whole thing up.

    3. I’ve seen this problem presented lots of times, and I always stumble on this aspect of it. If you don’t know how sturdy the box is, or how heavy the candle is, how long the tacks are, etc., how could you possibly know this will work? You’re just assuming that a paperboard box will cantilever with enough strength to hold the candle. I’ve always dismissed this answer outright as having too many potential problems to be a viable solution.

      1. I sometimes have this problem at work. I can come up with about twelve reasons why an idea won’t work. In the same time, somebody else has built a working prototype. It’s frustrating, and a very hard habit to break.

    4.  You only need one match to light the candle. Use the other matches in the book to build a truss underneath the box.

  8. I tore all the matches out of the matchbook, pinned it to the wall, folded down the top, pinned the candle to the top through the top, and then lit it.
    You even have a handy match striking surface that won’t get lost!

  9. Thumbtacking the box to the wall has been the correct answer for a long time but these days thumbtacks tend to come in hard plastic cases that tend to shatter so is the solution still relevant?

    1. Use the lighted candle to heat a thumbtack, melt holes with it through the plastic tack box, and use those holes to put the tacks thru. Voila! Where there’s a will….

  10. Poorly worded question.  In the solution, you’re not fixing the candle to the wall, you’re fixing the box to the wall.  The solution doesn’t answer the question.

  11. I got this right away, but I’m pretty sure it would have taken me much longer if the puzzle hadn’t come with a handy illustration showing the box. Actually seeing what you have to work with is a huge advantage over just a description, if you’re strongly visually-oriented like me.

  12. Lots of solutions here. Like some folks said, either move the table or just don’t light the candle. Or you could use a thumb tack to shave all the wax off the candle leaving only the wick which will burn very quickly but won’t drip.

    I don’t think the provided solution is accurate because it assumes the box is made out of paper, but wouldn’t work if the box were plastic, metal, or wood. Also, the question asks us to affix the candle to the wall, which their solution fails to accomplish.

  13. I suspect if I had the physical objects in my hands or in front of me instead of pictured, I would have thought of using the box as a resource.

  14. Burn it down. . .  the wall, the table, everything.  Then wax dripping on the table will be the least of your worries.

    I’ve always been a good problem-solver. . .

  15. It took me longer to work out which script I had to allow on the site to get the ‘reveal answer’ function to work than it did to work out the candle puzzle.

  16. Yeah, unclear.  The answer assumes that the box can be pierced by a tack, the wall can be pierced by a tack, and that the tack will hold in the wall under the weight of the candle/box.  Would only work with a cardboard box and a sheetrock or wood wall.  Personally, I’d have tried dripping wax on the tack heads, sticking them to the wall and pushing the candle onto the tack points sticking out of the wall.  Bet I could make that work.
    ETA: and use candle wax to fix the box to the wall under the candle to catch drips. More complex, and relies on the holding power of the wax, but it works for any kind of wall surface.

  17. There are similar experiments where you put someone in a room (or show a drawing of a room) and pose a problem that requires a piece of string or wire to solve. If there are pictures hanging from the wall, very few people think to take the picture down and use the picture hanging wire, but if there’s wire attached to the wall at eye height (instead of a picture), people get it right pretty easily.

    The box problem seems similar, although I must admit I only solved it when I looked at the drawing of what I had. With only the description, I probably would have gotten stuck. I also considered “move the table”.

    I wonder to what extent functional fixedness is an actual fixed phenomenon, or whether it can be deformed (broken) by awareness of it. 

  18. I’ve also noticed that 6- and 7-year-olds start to really get into rules and will demand everyone follow them.  For instance, it drives them crazy if you have fun with the lyrics of a song.  “That’s not right!”

  19. First, burn the table.

    Sweep away the ashes then burn the wall.

    Place candle on wall-ashes. Light candle.

    Burn person providing the objects.

    Burn the passers-by.

    Burn the trees.


  20. Oof, you guys obviously don’t know about OpenCandle or the candleBurn SDK. The solution is to lift the candle and look on the bottom. There are two small holes. Take one tack and place it in the left hole and hold it firmly in place. Now with the second tack you can enter the candleCode for the dripFunction you desire. The dripless function DripOption:0:release.wax:0 has the code “5E7F110″ After the code is entered you can light the candle in the routine way, I prefer to use the command line with GnumaCode CandleLight hashtags. Every decent candle uses that code set. If it doesn’t, well you are on your own, dude. Matches anyone?

  21. Don’t light the candle.  All done!

    Or tack the box to the wall, then tack the candle to the box with another thumbtack underneath .

  22. The correct answer is obvious, but Im not sure it actually works. Even assuming a suitable wall (something the thumbtacks won’t easily pull out of – not plaster) and a sturdy box (thick cardboard, say) eventually the box will contain a puddle of molten wax with a wick burning away in the middle – and then I suspect that the wick will burn through the cardboard, allowing the remaining molten wax to spill onto the table. There may even be a fire hazard. As mentioned above, the box is also liable to pull free as molten wax spreads across the bottom of the box and increases the torque on the thumbtack(s) holding the box to the wall, although this isn’t a problem given the right wall material and sufficient tacks used.

    On the other hand, if we had been told the box was made of, say, tin, I wouldn’t have any real concerns at all.

  23. For the people complaining that the tack couldn’t support the box… that can be dealt with in either of two ways.
    1: use more tacks
    2: place the box on the floor, then tack it to the wall, so that the floor is actually supporting the box’s weight, and the tack is only there to meet the requirement that you’re attaching it to the wall. after all, it doesn’t say that you had to attach it at greater than floor height.

  24. Tack the box in a corner of the wall, a tack on each of two sides of the box. Even better, if the box is rectangular, use two tacks on the long side. Takes care of most weak box problems.

  25. FYI:  This is based on Duncker’s (famous) candle problem, conducted as a psychology  experiment probably in the 1940s, and taught to every psychology major.  It was used to demonstrate ‘mental set’ or ‘einstellung’.  Subjects sat down and were given a box of tacks and a candle and matches, and so the box doesn’t stand out as something that could be used; it was seen as a container.

    I suspect that it wouldn’t be directly replicable anymore, because tacks always come in plastic boxes now, and giving someone a cardboard box of tacks would stand out as something strange.  You could give a box of matches though.

  26. The problem with this puzzles is that we’re not told what the box is made of. The box could be made out of steel for all we know. a better solution would be to melt down sections of the candle horizontally and pin it to the wall in different places. under the bottom pin, pin the matchbox in an L shape under the candle we know that matchbooks are usually made of carboard. Capillarty action from remaining matches could draw candle wax inbetween the matches thereby holding more. The solution isn’t foolproof but it’s better than pinning up the mystery box.

  27. Push building over on side. Tack building to ground to keep it stable. Place candle on wall that is now at the same angle previously occupied by floor.

  28. I am surprised to see how many people are evidently unfamiliar with this puzzle. One solution I’ve seen has you tack the  box to the wall by the bottom, so the candle is standing on one of the sides–somewhat handles the flimsy-box problem, though you still have to assume it’s some kind of cardboard. Also, this puts the candle pretty close to the wall. I like silkox’s idea of tacking the box into a corner!

  29. 1) Cut a hole in the box
    2) Put your candle in the box.

    Never mind, different box problem.

  30. The solution they offered came to mind right away, which made me think it had to be wrong – especially since I wasn’t sure the box could hold the candle or that the tacks would hold the box to the wall. But there’s nothing in the wording of the problem that says you couldn’t just rest the box on the table against the wall and then tack the box to the wall. 

  31. I was assuming the box was brittle plastic so you can’t use the tacks. My immediate thought was to glue to the box to the wall using melted wax, then put the candle in the box. This should work regardless of what the box is made of.

  32. I am impressed with the level of seriousness by the group in solving this problem. Here’s hoping we never face such dire circumstance in real life.

  33. Suggestion for Mark: next time, don’t link to the ‘answer’. Allow comments to vote up ‘best’ solution. Matter of fact, I don’t think bb has made full use of the ‘like’ feature of comments to brainstorm, has it?

  34. Light a match melt the side of the candle, while the wax is hot stick the candle to the wall. What your worried about wax dropping on the floor? Your just stuck a wax candle to the wall.

  35. Looking at the preferred answer for this, as soon as the candle burns down to the box it’s going to set it on fire and pour flaming cardboard and molten wax onto the table.  Which would be entertaining but not the desired outcome.
    Solution #2: Download ‘Flashlight’ app for smartphone. Set phone on table, using sophisticated 21st century multipurpose communication computer as, basically, a flame.
    Feel superior. Sneer at low tech candle, matches, tacks, box.

    1.  not if you set it on the flame-retardant matchbook lid, inside the box. Plenty of spare tacks to stabilise it.

  36. Before I read the solution, I admit I never considered the box.

    Use a pin to score/cut half the candle away. Pull the wick out of one half of the candle, then use the sharp tip of a tack to cut the wick. Now you also have a string to use.

    Remove the matches from the book. Use one thumbtack to pin the lid of the book to the wall, another to pin the bottom of the (now shortened) candle-top to the other half of the matchbook. Push pins through the removed wick and use to secure the candle to the wall. If necessary, use a third pin through the wick to the candle to give the matchbook some extra support.

    I was a bit skeptical of this solution, but I think I still trust it better than just pinning the box to the wall!

  37. I thought of the “correct” answer quite quickly as well, but I was concerned that any box that can be held to a wall by thumb tacks would likely be too flimsy to support the  weight of the candle.  I kept trying to think of some way to add structural support (maybe using the match sticks?).  But, according to the solution, I was apparently over-thinking things.

  38. I guess I should be proud. I immediately noticed the box and wondered why you would need all of those thumbtacks and matches.

  39. Using nine tacks in sets of three: use two thumbtacks from each set of three to tack the third tack to the wall with it’s pointy side out. Then do the exact same thing with the other two sets of tacks, creating a vertical line of three sharp tacks sticking out from the wall.

    Push the candle into the tacks so it’s held vertical.

    Place the box underneath the wax to catch the drips.

    Light the candle.

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