It’s the Friday Puzzle!


First, the big news is that the website for my new book, Paranormality, has just launched here and contains a nice little video to put a chill up your spine.  The book can be preordered from Amazon at 50% discount here.

UPDATE: Paranormality now the top selling popular science book on Amazon – thank you all so much!

Second, there is lots happening over the next few days.

– On Saturday I am speaking about the psychology of self-help at the School of Life.

– On Monday I am speaking at the Sheffield Skeptics in the Pub.

-On Tuesday I am talking about jokes at the British Library.

OK, here’s the puzzle.

What is the missing number (oh, and the 7 is not a typo)?

As ever, please do NOT post your answer, but feel free to say if you think you have solved it and how long it took.  Solution on Monday.





130 comments on “It’s the Friday Puzzle!

  1. Craig Morgan says:

    Got the answer in about 45 seconds.

  2. Pseudonym says:

    If only that last number were 8 instead of 7…

  3. Meg says:

    Figured out the pattern in about five seconds, and the answer in a further half a minute.

  4. wraakh says:

    less than a minute… and it’s not even 7am 🙂
    Made my brain wake up though, thanks.

  5. mklprc says:

    Certainly a weird way to express it, but simple when the pattern is discovered.

  6. Stephen M says:

    I think I solved it, but shouldn’t the last number be 8 instead of 7?

    • Pseudonym says:

      I suspect that most of the people who said they got it quickly didn’t check their solution carefully.

  7. Stephen M says:

    @Pseudonym: It’s really weird that our theory would work for the whole series but the last number… and that we’d be off by 1. I mean what are the odds?

    But you’re right, I suspect the others didn”t check their solution carefully either.

  8. fluffy says:

    Yeah if the last number were 8 that would be freaking trivial. But it isn’t. The obvious one also doesn’t seem to have anything to do with the arrows, so there might be something triiiiiiicky going on here.

    • Stephen M says:

      I think my theory accounts for the arrows pretty well actually. But maybe we’re not talking about the same thing 😉

    • wraakh says:

      hahaha, how does my brain work when I had to go back and look for you’re pattern expecting an 8 🙂
      The other pattern (that works on all of them) seemed more obvious to me… which I honestly find really strange right now.

  9. Debayan says:

    I expected the last no. to be 8. Damn! I’ll have to go again.

  10. Bruce says:

    Yeah, had the ‘easy’ (but incorrect) one in about 20 seconds. With another 10 seconds before I was disappointed. Getting to the real aswer took about 2 minutes more.

  11. Pseudonym says:

    Oh, and yes, I did get the correct answer after a couple more minutes.

  12. Rob J says:

    Got it!

    Got the “obvious” wrong answer immediately. Read some comments, realised my answer was wrong. Looked again, couldn’t do it. Hit refresh a few times, read some more comments, tried again. Couldn’t do it. Hit refresh a few more times, and eventually got the answer. I don’t think any comment gave it away for me, but I am happy that I have the right answer now (after 10 minutes or so).

  13. barefoot dan says:

    That took me far to long to work out, about 5 minutes just staring at it before it suddey clicked

  14. Yogzotot says:

    Yep. Immediate (wrong) solution in less than a minute, correct solution (i.e. a simple one that works) in another minute.

  15. JayCee says:

    Trcky indeed thanks for the comments, otherwiese i would not have read to the end and have the wrong answer. Now after 6-7 minutes i have an answer which fits in the whole chain.

  16. Kagnon says:

    About 5 minutes.

    A really tricky one this time.
    Got the easy one at first until i noticed the ending later on.

  17. Ambar says:

    Took me 10 to 20 sec. The easiest one so far!

  18. Ambar says:

    Ok! No! It’s not that easy!

  19. Tomas says:

    By coincidence, I solved this puzzle just a few days ago. I guesstimate it took me about 30 minutes. Maybe it should be pointed out that the 7 is not a typo.

  20. Linzi says:

    Under 30 secs… Who says strippers are thick!?!? 🙂

  21. This was way to easy about 20 seconds or something.

  22. Dave says:

    I got this one pretty well instantly.
    It’s good that the puzzles can reflect the ability range of your followers.

  23. T9sus4 says:

    Took me a minute, nice to get the brain going in the morning.

  24. this not seems to be a puzzle of your type…

  25. yrnkrn says:

    Very nice… two minutes.

  26. Got the solution is less than a minute. I don’t see the problem with the last 7 – it fits my pattern just fine.

  27. vivian says:

    saw the pattern immediately, took me about 30 seconds to verify it and calculate the answer.
    (it usually takes me much longer and i’m terribly frustrated to read other people commenting that they found the answer in 2 seconds…)

  28. Jim Cliff says:

    Clever. Got the wrong answer in about 20 seconds. Took me another minute or so of staring at it before I spotted the real pattern.

  29. FlorayG says:

    easy. Got it in ten seconds – much less controversial than last week’s puzzle!

  30. FlorayG says:

    oh no no no – I just saw that number 7 – back to the drawing board – I thought it was a bit too easy…

  31. Bren says:

    Clever. Got the right answer after about 2 mins. Then read the comments and just had to go back up to figure out the wrong one!

  32. FlorayG says:

    got it got it got it! ten minutes. I’m so chuffed (although I usually get these quicker, I was fooled by the ‘obvious’ answer)

  33. ChivNick says:

    Got it (half hour on and off) – the number 7 is not a mistake as some posters are suggesting.

  34. Joao Pedro Afonso says:

    Got it. Took me 15 minutes of useful time and had to use pencil and paper, but got it. Head was not enough. Wonderful puzzle.

    • Joao Pedro Afonso says:

      Wow! I wrote the first thing that come to my mind, without seeing any comments (to avoid contamination), and my “got it” repeat the last 2 comments? What are the odds of that? The world is indeed small.

  35. Sean Ellis says:

    I got this on my first guess, pretty much immediately.

  36. Casper H. says:

    Took me about 3 minutes after 1 minute for the wrong solution. Nice one, I have to say.

  37. Vjera says:

    30 seconds. Easy!

  38. lilabyrd says:

    Deer in headlights……………………aaaahhhhhh…..splat…thump…..

    • lilabyrd says:

      All weekend off and on this thing has bugged me….came up with a number not sure how I got it went back and forth, forward and reverse… so I will see in a little while….

  39. mittfh says:

    Sneaky! I ‘got’ the obvious solution within a few seconds, then did a spot of maths to verify.

    As for the ‘real’ answer, I’ve got one that involves the same mathematical operation, but treats each number slightly differently to convention.

  40. MiniKeb says:

    I tried during arround less than 5 minutes and I found the correct answer and I don’t need to change the 7 on the right side by an 8.
    Can I say that the answer is a number with 2 digits?

  41. mickeyd says:

    Got my about 5 minutes after coming to the wrong solution in 15 secs…

  42. Emlyn says:

    At last! I got the obvious (wrong) answer as I was reading it. Then once I realised it was wrong it took about 5 minutes of trying to get the wrong answer out of my head before I got the correct answer.

    • Andy says:

      Brilliantly put Emlyn

      “At last! I got the obvious (wrong) answer as I was reading it. Then once I realised it was wrong it took about 5 minutes of trying to get the wrong answer out of my head before I got the correct answer.”

  43. sharedvoids says:

    Oh dear, that took far too long (about 10 minutes) considering how simple it turns out to be!

    The wrong answer (with 8 not 7 in the last box) was so much quicker…

  44. Barmonger says:

    First guess took 10 seconds but was obviously wrong.
    The real solution probably took me around 5 minutes 🙂

  45. writerJames says:

    I suppose it’s too much to hope that the 13’s a typo?

    Hmm, I’m still puzzling.

  46. Will says:

    Well I have got a solution that works but it is not particularly elegant so I very much doubt it is the one we are supposed to get.

  47. Wolf Martinus says:

    That was a nice puzzle. Took me about 2 minutes to find the wrong solution and probably almost 10 more for the right one.

  48. Anne says:

    It has only taken me 2 or 3 hours to not get the right answer. Took about 2 or 3 seconds to get the wrong one. I’m not as clever as the rest of you!

  49. Anonymous says:

    Ha ha!!
    As the rest of of the peopole here… I first find this really simple but wrong solution – then this even simpler and correct solution! Nice!

  50. Luis says:

    About 10 seconds

  51. Berber Anna says:

    Got it. Looked at the decoy for a few minutes, got stuck, so I came back after a while to look at it again and it immediately clicked. You just need to put the ‘8 solution’ out of your head completely.

  52. Doug says:

    LOL. Funny. Took about a minute or two of head scratching.

  53. Rob says:

    Took two goes, very clever puzzle. Who the heck thinks these things up!?

  54. Walt says:

    If I am correct as to the missing number, that would make the 7 in the final circle incorrect.

  55. Dennis says:

    Coincidental to the last number being not the easy 8, it took me 8 minutes.

  56. nanda says:

    30 seconds

  57. Kate says:

    Well, it’s taken me a couple of hours on and off, and one number keeps popping into my head. I have no idea why, can’t work it out, but I think it’s the right number. Like a few others started out on the wrong track. I’m certainly not finding it easy….

  58. Marion says:

    I have no idea about this one, have been looking at it for an hour or so and think I will have to come back another time. I am also drawn to one number but am not sure of the reason. I will have to keep thinking..!

  59. Robert Johnson says:

    Easy (but wrong answer) about 1 minute. Correct answer about 2 minutes more.

  60. Boulet says:

    Got it !
    It’s a VERY GOOD one ! If I hadn’t read the “7 is NOT a typo” I wouldn’t have got the answer right !
    Same as Robert Johnson: obvious but wrong answer in about one minute, correct one another minute after realizing the first one was wrong !

  61. Bernhard says:

    where fast on the wrong to the “8” solution gave up for a time, read comments and found the right answer after reading “mittfh” ‘s comment…

    The hardest Part is to get the “8” solution out of the head…

  62. faza says:





  63. Shan says:

    Man!!!! it almost drove me nuts…… But i have finally cracked it 🙂

  64. Very cool. I wonder how much work went into the misleading pattern?

    I spent a minute or two on the obvious but wrong solution, then another couple of minutes until I was able to think sideways enough to get the right angle. Maybe five minutes total processing before I had the answer.

  65. Stu says:

    Took me about a minute, but I was surprised to stumble on a working solution that quickly. Discarded the incorrect pattern immediately thanks to Richard’s hint.

  66. Amalia says:

    30 seconds for the carefully designed wrong answer, then 5 more minutes “trying”, 1 minute to realize that I had to make the “7” work, and then 20 seconds.

  67. Danny says:

    took less than a minute

  68. cor says:

    I thought i was a dumb nut not figuring it out. got the wrong answer first, was stuck that operator.

    VERY tricky one, especially working in such a confusing pattern must have taken quite some time!

  69. grimtrigger says:

    Although pretty simple, I like this one. It’s kind of like an illusion… you see two different things before figuring which one is the ‘intended’ image.

  70. Anne says:

    Six or seven hours (on and off) hard thinking and I have managed, at last, to still not get the answer. Getting ready to kick myself when the answer(s) are published!

  71. Marilu says:

    This one was easy, got it in about 10sec!… the part i don’t understand is why will i think that the 7 is got to be 8?:s

  72. winwardo says:

    Haha, as everyone else, was very quick with the “wrong” solution.
    Took me about 10 minutes to complete it after mittfh said they treated the numbers differently than normal to find the answer.

  73. Punkage says:

    Took ages to get the 8 solution out my mind…about 30 minutes to finally get it

  74. Martin Paskalev says:

    Whew! I finally got it! It took me a little while. Wait and see 🙂 Regards

  75. Sue Morgan says:

    Got it in less than a minute ~ but my brain is wired for numbers/math/patterns.

    No idea why.

    the written word? Dyslexia stinks sometimes.

  76. Julia says:

    kept thinking along the right lines but – as usual – assumed it had to be more complicated and only got the right answer after about 15 minutes (with the first 5 minutes spent on the wrong answer that everyone else has got).

  77. Jerry says:

    About two minutes. One rule seemed to work until the rightmost number, but the second worked for all numbers.

  78. Anders says:

    Wow, that took forever. Once I saw it, it seemed obvious, but it took ages to get to it. Something like 12 hours

  79. Anders says:

    By the way, it’s good to see a puzzle that actually exploits the brain’s ability to seek patterns that aren’t there, and challenge standard assumptions – so much better than trivially bogus and incorrect pseudo-statistical problems. Well done

  80. says:

    YAY didn’t see anything on first glance, then read the comments, got the correct answer after about 30 seconds of looking at it again, then wondered what all the fuss about the *wish it was an 8* comments, then saw how easy it was to confuse the two!

  81. Stephen Williamson says:

    Got the correct answer immediately. I haven’t gone back to puzzle out why so many people thought the 7 was a typo though.

  82. The other Matt says:

    Got it in four minutes. I think it will be correct. If so, then this puzzle is a little bit nasty and will get many, many comments on monday !

  83. jimthehedgehog says:

    Aargh! Looked at it this morning and got the “obvious” solution that would require the last number to be 8, then came back to it this evening after some beers and the correct solution jumped out at me. If anyone is having problems solving this then I recommend a few pints of Tanglefoot 🙂

    • Michael says:

      Well, I had a couple of glasses, and I decided to invoke my own rule to account for the “blip” of the last iteration, justified by the fact that it’s the only single-digit number.

      I will call that sufficiently parsimonious. Who’s gonna say I’m “wrong”?

  84. shortcinema says:

    When does the book come out in the US?

  85. Tan Coul says:

    4 or 5 minutes – so easy to get hung up on the obvious wrong answer it’s easy to imagine that the right answer must be a very complex formula…

  86. vertext says:

    took me like 10 minutes. the last number not 8 puzzled me all that time till eurika moment came :d but very confident about my answer

  87. namowal says:

    MY GOD, I got it in a few minutes- and I’m a dummy at math.

  88. mjr256 says:

    Hope you can make it to NECSS this year.

  89. Anonymous says:

    Got it in about a minute

  90. Simon says:

    Stumbled first time . Got it now. Really really liked this one!

  91. slightly_skeptical says:

    Wrong solution easy, seconds. Right solution about an hour. Tricky.

  92. 7 of 9 says:

    Got it in 2 milliseconds!

  93. Juan says:


    I got it in my second try. And no, the number 7 is correct. 🙂

    About 5 minutes in the correct anwer, seconds in the bad option.

  94. Danielle says:

    Easy. Got it in under a minute.

    I don’t see why the last number would be 8 – maybe it has to do with the fact that I figured it out by reading the sequence backwards.
    I think the obvious-but-wrong solution has escaped me this time. (it’s a first!)

  95. Cosmin Romania says:

    I managed to get the solution in 2 minutes 🙂

  96. UXO says:

    Good one. Still a bit too easy, but a big improvement over the last few algebra-only ones!

  97. Neil2Russell says:

    ARRGGH – Can’t believe it took so long to get the answer. Probably about two hours on and off. Couldn’t get the wrong answer out of my head. So simple when you get it.

  98. erica says:

    Had to run through about five different hypotheses before getting it.

    Very neat, very sneaky. A puzzle with a sort of trapdoor that drops the mind onto the wrong track.

  99. Hyanur says:

    Got it after 2 minutes 😉

    The second try was the right version…

  100. Craig Morgan says:

    Like most, my first answer was the red herring pattern. Spent another 10-15 minutes on it to arrive at a solution that works for the whole puzzle.


    After seeing the 7 vs 8 problem, I immediately convinced myself that ‘nature’ of the solution would not be along the same lines as the red herring pattern. I knew I would have to (as Timothy Mills said) think sideways. So I started on the right, rather than the normal left-to-right reading.

  101. katie k says:

    Oh, brilliant!

    I, like so many others, got the wrong answer immediately. It made me all frustrated, so I decided to close the page, clear my head, and try again the next day. And I got it!

    The ones you have to work a little harder for are always the best.

  102. Yaw says:

    Oh what an interesting question! Nice~ But as per all questions, when you got the answer, you know you got the answer.

  103. fmo says:

    the trapdoor comment is spot on! i had a hard time climbing it out of it until a friend pointed out looking at it from a different, more adventurous perspective!

  104. JJ says:

    I wish Paranormality – indeed, more of your books – were available on the Kindle.

  105. Anonymous says:

    Its for genius like you:
    6 and 2 = 22
    4 and 3 = 1
    8 and 2 = 46
    Then what is the answer of:
    7 and 2 = ?
    reply fast.

  106. Anonymous says:

    Give me a hint here.

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