It’s the Friday Puzzle!


For those who missed it, Channel Four’s recent ‘Derren Brown Investigates…’ can be seen online here, and features my good self chatting about cold reading.  I have a feeling you are the sort of person that will enjoy the programme.

OK, to the puzzle… I have to make dinner and have to boil some pasta for exactly 9 minutes.  However, I only have two hourglasses.  One of them measures 7 minutes and the other measures 4 minutes.  Can I use the hourglasses to time exactly 9 minutes?

As ever, please do NOT post your answers, but do say if you think you have a solution and how long it took.  Answer on Monday.  Make the most of Saturday.  It is due to rain on Sunday.

137 comments on “It’s the Friday Puzzle!

  1. Aseem says:

    This one was easy… have come across many similar puzzles involving hour glasses… solved in only one minute.

    • ScreamingGreenConure says:

      ooh, sorry, so close but so far – my -6 hours (approx) beats your 1 minute!

    • fluffy says:

      @ ScreamingGreenConure we’re so proud

    • ScreamingGreenConure says:

      I know it sounds like a blessing, but having an IQ of over 9000 can be a curse in many ways. It’s appreciation from people like you that make it all worthwhile, Fluffy. Thank you.

    • lilabyrd says:

      ScreamingGreenConure…….I know what you did… left finger prints…..hehe
      {at my place I posted a new photo of my green cheek conure…ole’ loose lips himself!}

    • ScreamingGreenConure says:

      I did it with SKILLS.

  2. JB says:

    I got it! It took about 20 minutes of thinking.

  3. ScreamingGreenConure says:

    I solved this last night. I’m not joking, I had the answer to this six hours before it was posted, so I’d say it took me -6 hours to come up with a solution. I don’t know why the rest of you are lagging behind, but I guess this basically makes me your rightful leader.

  4. Steve Ulven says:

    I’ve solved this problem a few years ago, but it took me a couple minutes to resolve it.

  5. fluffy says:

    Got it pretty quickly. 30 seconds or so, would have been quicker if I wasn’t feeling so anal about the little diagram I drew.

    • ScreamingGreenConure says:

      I have to say, I didn’t do a diagram. I took a nap instead. You can be my second in command.

  6. Sam says:

    For once I got one of your puzzles straight away!
    These kind of puzzles always make me think of Die Hard 3….

  7. Daniel says:

    couple of seconds to solve it

  8. Brian G says:

    Yep, you can indeed

  9. Had to verify my answer again so had to redo the math. Took me less than half a minute.

  10. t9sus4 says:

    Solved instantly.

    • M says:

      Are you sure? You cannot boil pasta in exactly 9 minutes with intervals… Because i think you’ve got that answer.

    • ScreamingGreenConure says:

      INstantly is not as good as 6 hours in advance. Sorry.

  11. Mark says:

    Oooh that had me pondering. About 4 minutes. My initial thoughts stumbled on the fact that the egg would have to be timed continuously and my answer didn’t allow for that. Once I had got past that it was much easier!

  12. Scottmacs says:

    This one took me longer than usual…about a minute an a half.

  13. Nick Sharratt says:

    Phew, got it eventually after a couple of minutes. I was trying to make it over complicated initially.

  14. Earl says:

    Easy one – 10 seconds.

  15. James says:

    Actually managed to get this one pretty quickly (for me!) – less than a minute.

  16. Joao Pedro Afonso says:

    we surely can… time to solve: less than half minute after read.

  17. Liam says:

    Did not take very long ~1min. I kind of knew what the solution consisted of already (a la Die Hard 3). Took me a while to find a pen with ink and write out a solution.

  18. Yes very good . Solved around 2 minutes.

  19. ruth says:

    Grrrrrr, this is driving me nuts. Can only get 8mins. Ultra al dente pasta anyone? Have 3 hour drive this afternoon – need to solve it before then or the drive will be one long headache!

    • Sam Rothstein says:

      “Can I use the hourglasses to time exactly 9 minutes?”

      If you’re having trouble just have a guess… It’s got to be Yes or No!

  20. LongSteve says:

    However our brains are wired, my wife and I combined are pretty good at these sorts of puzzles, and it took us about two minutes of discussion.

  21. Vincent says:

    Got it.
    Took me slightly more than 5 minutes.

  22. 8 minutes. I think that’s about my limit. Any longer and I might have given up. Or read the comments. Which is practically cheating. Having said that, I haven’t read the comments yet, as that would have been cheating.

    • ScreamingGreenConure says:

      the only important comment is mine, informing you I did this several hours before it was posted, and therefore I am king.

  23. lilabyrd says:

    Uh, anyone know where I can find a couple of hourglasses one a 7 minute and one 4 minute? I need to replace Richard’s……I broke them and need to put them back before he finds out I was there and broke them…..AND SCREAMING GREEN CONURE YOU LEFT YOUR FINGER PRINTS ALL OVER HIS PLACE ….. SO I KNOW HOW YOU GOT THE ANSWER SO EARLY!!!!……..LOL…….

    ps. I got the answer in -2 minutes….haha

    • ScreamingGreenConure says:

      I don’t even have fingers.

    • lilabyrd says:

      Hey no fair SGC you started drinking early……now we will all have to try and catch up…….it will be hard work but I’m up to it!

    • lilabyrd says:

      Oh my, I ask for forgiveness oh great SGC as I now see I have misjudged your jubilation with intoxication since I was overcome by your brilliance……beg pardon!

      so can I have a ride in your tardis…please!

    • ScreamingGreenConure says:

      Is that a chat-up line?

    • lilabyrd says:

      SGC oh yeah….lol…right….but only if I can go and see next week’s puzzle…I won’t tell anyone…..OK everyone close your eyes and plug up your ears cause I don’t want you to know I may sneak into next week…..hehe….

  24. Ed says:

    Got the one that I suppose Richard is thinking of.

    But then I’ve also found a slightly sneaky alternative that gets you your pasta a few minutes sooner!

    Anyone else get that? Will post on Monday…

  25. It took our collective minds about 10 minuets.

  26. Mike Torr says:

    Took me 13 minutes for some reason. I’m normally quicker! I think there is a slight erroneous assumption in the puzzle, that would make this less than a 100% accurate method – but still good enough for cooking pasta 🙂

  27. Vern says:

    Solution took 9 minutes – DUH!

  28. Nicola says:

    I ran into similar puzzles several times before… so it took me less than a minute

  29. ruth says:

    Went away for a shower and got it as soon as I came back! Hurrah. Shouldn’t make assumptions and give myself unnecessary constraints 🙂

  30. Alex says:

    I think I’ve found two solutions to this. I don’t think it’s possible for it to be absolutely accurate, but then, nor are eggtimes generally.

    Took me around 10 mins to find the first, and about another 10 mins later I spotted there might be a second.. And then 5 mins to make sure.


  31. FuzzyDunlop says:

    I have to be honest, this took about 30 seconds. It was more about doing the sums than the method.

  32. Leon says:

    took a couple of minutes, the answer isn’t as obvious as I initially thought it would be, nice puzzle, thanks for them, they make a good start to fridays!

  33. Al Dente says:

    Boil the pasta for 7 minutes, then keep testing until it’s al dente, or to your taste. The timings on pasta packets are usually wrong anyway… 🙂

  34. DaddyLouLou says:

    About 20 seconds to think of the solution, and a minute to write the proof.

  35. Aubrey says:

    I think I have an answer, but it’s not terribly ingenius. Took about a minute.

  36. Anne says:

    It took me a few minutes because I wasted time drawing a picture to prove the answer

  37. It took me about a minute (timed using one 5-minute egg timer, an elastic band, and a sundial).

  38. Cuneiform says:

    Circa 20 minutes this time.

    I wonder how diagrams or elaborate math could help with this puzzle – basic plus, minus, divides, multiplies will do.

    • ScreamingGreenConure says:

      Sometimes you just have to draw a picture. It doesn’t even have to be relevant, you get the urge.

  39. Ricardo says:

    Optimal solution?
    The solution I have takes 12m to setup before starting to cook. What is your setup time?

  40. MarKill says:

    Ok I have the solution but what a silly way to time 9 minutes

    And not to be annoying, I never time my pasta as it is never ready if you keep to the time on the package. I’m thinking it’s a conspiracy

    Anyway I would stand next to it to test it instead of time it

  41. Myk says:

    Yep. Somewhere around a minute. I really should get a stopwatch on these.

  42. Iain says:

    I believe you can start cooking sooner…

  43. Olaf Buehler says:

    Got it. About a minute as well.

  44. Matt says:

    Oh yay, finally one that doesn’t take me hours to work out. Got it in 5 minutes instead.

  45. Finnur says:

    Solved in about 20 seconds. I normally can’t solve your puzzles. So it’s a big day for me.

  46. Anonymous says:

    Tricky, but i think i got it. Took me a couple of minutes.

  47. alok says:

    i solved it in ca.25 m.

  48. alok says:

    there are 4 steps to follow.u have then the solution.

  49. Berber Anna says:

    Got it, but only after reading the comments. Ricardo and Myk sort of gave it away.

    • ScreamingGreenConure says:

      Yeah, but who got it EARLY, hm?

    • Berber Anna says:

      I bow to your greatness, oh ruler of all pasta-related matters. Though I speculate you only got it early because
      a) you always use non-accurate egg timer things when boiling pasta
      b) you own a TARDIS. In which case you are obviously awesome by default, and I will bow some more.

    • ScreamingGreenConure says:

      haha, yeah, that’s it.

    • ScreamingGreenConure says:

      Actually, I got a whole crowd of people and listed all the earlier puzzles in order and had them examine the chart. After some group bonding, I got them to come up individually with their guesses as to what the next puzzle would be. I collated the responses, and came up with this one, which I then solved.

  50. Alessandro I. says:

    Of corse you can, and is not difficult!

  51. Mike Torr says:

    As people seem to be interested in this, I just wanted to add that my solution has NO setup time. You just begin.

  52. BigBadEd says:

    A little under 2 seconds

  53. Timdifano says:

    OK done in a couple of minutes to get 12 min setup time …I think it would be more practical to taste the pasta and cook accordingly, but less fun.
    Now to get the set up time down…

  54. Marcello says:

    Yes, got in around 2 minutes.

  55. David says:

    Took me a while to get this but finally got it after pausing for a few minutes.

    I’m not sure where I developed this mental crutch but I could only get the answer after I saw that others had gotten it. 😦

  56. David says:

    Agree with Mike you don’t need any setup time.

  57. darthtanion says:

    I figured out what sort of thing I was supposed to do pretty well straight away. Took a couple of minutes to figure the answer.

  58. BeamStalk says:

    A couple of minutes.

  59. Todio says:

    Solved in about 1 minute. I’m not generally that smart so perhaps I’ve heard this one before or one similar?

  60. Petros says:

    Saw it straight away. How odd!

  61. bananacat says:

    It took me about two minutes to reason it out and then check my answer, and I’m fairly certain I got this one right. I guess I’ll see on Monday.

  62. killyosaur says:

    Got it. about 5 minutes.

  63. Craig says:

    Solved it with 8 mins setup.
    now scratching my head over this 0 mins setup business…

  64. Cuneiform says:

    Interesting, I initially had a solution with necessary setup time. After reading in the comments that there is a solution without, I figured that one / such a solution out too. And that one is actually simpler too exercise, and was simpler to come by.

  65. Berber Anna says:

    I did initially think of a no-setup solution, but that is entirely dependant on the accuracy of the egg timer, so I discarded that one. Can’t think of one that would work without knowing more about the timer. Probably not smart enough. 😛

  66. D says:

    Five minutes. The answer was not as elegant as I had hoped, but it works…

  67. McQ says:

    I too, thought of “Die Hard 3” when I saw this puzzle. I think that actually threw me, because I wasn’t sure if the solution should be worked out the same way.
    About a minute of thinking confirmed it to be ok, at least I think so!

    So I got it in about a minute. We’ll know for sure on Monday.

  68. Eddy says:

    About a minute. My solution seems overly complex, so I’ll probably spend another couple of minutes convincing myself I didn’t miss an easy answer. This is the 12 minute setup time answer, so scanning other comments makes me think I DID miss the easy answer… darn.

  69. jh says:

    I got the answer in which you need a setup time in a couple of minutes. Then I read the comments saying that in was possible with no setup time.
    This answer took me some good 5 to 10 minutes!






    Would not work with all types of egg timers.

  70. Hal says:

    Do you wait until the water returns to a boil before starting to time?

  71. Lumpy Jay says:

    I finally got it after half an hour!! doh

  72. Rachel says:

    I have the 12 min set-up answer. Took me a couple of minutes thinking and then a while writing it out. Now, I

    a) cannot be bothered finding a more elegant solution.
    b) bow to SGConure’s obvious and awe-inspiring mastery of all known phenomena, and several of the unknown.

  73. Rachel says:

    Update: oooh, I get it now. The no set-up time version. And, since I didn’t even have to think to work it out, instead using Google, I must surely win the internets.

    • ScreamingGreenConure says:

      Haha, ok, I am lord of everything else but you can win at internet.

  74. Z says:

    Got the no-setup version in a matter of second, basically I lucked out and it was the first thing I thought about.

  75. Jo says:

    I am not sure why some answers talk about egg timers and set up time… Richard did state hourglasses, and of course the time would have to be continuous, or it would not really be timing a nine minute cooking segment. This one was pretty easy…

  76. TS says:

    No you bloody heck can’t!!!

    Food is all about taste and texture. You need to check your food as you cook and in the case of boiling pasta, ensure that the consistensy is to your prefence. It’s what seperates us from the animals… well, that and opposable thumbs.

    You should really know better with all those celebrity chefs in the media.

    • ScreamingGreenConure says:

      I know, right? Heston Blumenthal would be shaking his head, and Gordon Ramsay would still be screaming obscenities after reading this.

    • TS says:

      Actually, Heston Blumenthal would probably try out the timer thing first and then abandon the idea in favour of a pasta density testing device 🙂

    • ScreamingGreenConure says:

      He’d make the pasta out of elephant testicles

    • TS says:

      But only after tasting the original ingredient that the Tudors would use, Wolly Mammoth.
      He found the taste too “hairy” and besides, he wants his produce to be fresh and not frozen.

    • lilabyrd says:

      I’m not sure I’ll ever be able to get that image out of my head…thanks both of you……sick….sick…sick…..but most likely….true……….

  77. Robert L says:

    flip flip flippy

    took about 30 seconds!

    fun little puzzle!

  78. Zach says:

    Richard, your pasta’s not going to taste much different if you boil it for an extra 2 minutes. But if you want to be a stickler, here’s the 2-step solution:

    1) go out and buy a digital timer
    2) use it

    Cheers! (I’m not British but I love that word).

  79. Ken B says:

    Can I use the hourglasses to time exactly 9 minutes?

    I answered that instantaneously — “yes”. 🙂

    Oh, you wanted to answer “_How_ can I use the hourglasses…”. I’ve seen similar puzzles before, so it took me about 30 seconds to answer this one.

  80. Mervulon says:

    No you cannot.

  81. Michael Kingsford Gray says:

    Got an answer. In about 1½ ‘
    Can’t say whether it is ‘yay’ or ‘nay’.

  82. Tommy says:

    The Derren Brown program can only be seen in th UK I guess?

    “The service is not currently available in your area”.

    As for the puzzle; the answer is a waste of time, if you know what I mean.

  83. Tom says:

    took a few seconds

  84. Anonymous says:

    Easy if you think

  85. Aristicanne says:

    Took me 3 minutes… Start both 4 and 7 timers at the same time. When 4 has finished, turn it over to set again. When 7 has finished… start cooking (1 minute still to go on 4 min timer). Make sure the water is boiling before you put the pasta in and don’t forget a drop of olive oil! When 4 min timer stops after 1 min, set 4 again and then again. There are Italian restaurants – it might be an idea to source a good one.

  86. Soulfull says:

    less than 1 minute…the answer is there to everything, we may just not have found it yet…

  87. Adan Ova says:

    Got it in like… two minutes.

  88. Jerry says:

    I got the concept immediately: Use one timer to time the other. All I needed was to get the right sequence of hour glass flips. I went to bed and in the minutes before falling asleep. I hit upon the solution, which I amazingly remembered on waking up Saturday morning.

  89. Jerry says:

    Those of you who wait seven minutes before starting to cook the pasta should think again and you will find a solution that allows you to start the pasta and the timing simultaneously!

  90. Andy says:

    This puzzle reminds me off the water puzzle from Die Hard With A Vengence.

    There is a bomb by the water fountain (in central park), Bruce Willis and Samuel L Jackson need to find a 2kg weight to defuse it. They are given both a 3 litre and a 5 litre container – how do they do it?

  91. phoebe says:

    pretty easy but its quite a good puzzle. Figured it out in say 20 seconds

  92. Ryan Kon says:

    Solved it in less than a minute. 🙂

  93. BillWhite36 says:

    1/2 sheet of paper – no answer.
    Went to check last week’s puzzle, whikch I had not gotten and didn’t understand the answer for quite a while.
    Came back to this and solved with 5 “movces” on paper.

  94. Engywuck says:

    I think I have solved a similar puzzle years ago. So it took less than a minute to come up with an answer for this one.

  95. Mark says:

    Yes! Finally after months of trying I have finally solved a Friday Puzzle. Took about 5 minutes.

  96. Reppy says:

    Got it. Took me two days.

  97. grimaud50 says:

    I think I solved this one quicker than any before – just a few seconds. Maybe my answer isn’t what was intended (since I was done so quickly), but it would work!

  98. Marion says:

    It’s now very early on Monday morning and I’ve had a very busy weekend. This is the first opportunity that I’ve had to look at this puzzle and I can’t get it because my brain isn’t working now.
    My pasta will be ready when it is ready and if you don’t like it cook it yourself!!

  99. Samara says:

    I found the solution. Took me a while..

  100. Alek says:

    think i got it – 3-4 minutes.

  101. […] 18, 2010 It’s the Friday Puzzle! Today I have to make dinner and have to boil some pasta for exactly 9 minutes. However, I only have […]

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