What value should ‘x’ be in the following sequence?

16 06 68 88 x 98

As ever, please do NOT post your answer, but do feel free to say if you have solved it and how long it took. Also, it is ok to leave fake/joke clues (but no real ones!). Solution on Monday!

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.


    1. I misread the question as “should ‘x’ be in the following sequence. That confused me for a moment but when I had the right question, I solved it pretty quick (around a minute) and even instantly thought of how to write the answer BECAUSE of my misreading of the question in the first place…

  1. Not sure if I have the correct answer but if I have, it took me 3mins. Slooooow compared to everyone else, huh? šŸ˜€

  2. Took me about two minutes – I’d like to say it was very clever, but I actually felt like a bit of an idiot when I found the answer!

  3. I normally don’t like those kinds of puzzles. But this one was easy to get my head around after about a half minute

    It can even be solved on small phones, as long as they aren’t too much down to earth.

  4. I feel a bit slow now reading those comments. Love the Friday puzzle, this one took me the longest so far.

    Equally pleasing and irritating when you get it though.

  5. About 30 seconds of looking for a pattern before I spotted what was going on.

    While it’s possible to construct a formula to generate that sequence with almost any number at x, I think, having found it, it’s obvious which one the problem setter had in mind.

  6. Got it in about 60 seconds, but only because I wrote the sequence down on a sheet of paper in a single column, (hint!)……

  7. quite simple, really. If you take the function

    f(x) = 11 x^6-3476 x^5+417956 x^4-23727440 x^3+639051776 x^2-7194463232 x+24770887680

    and solve for all f(x)=0 you find that x= 16, 06, 68, 88, 40, 98

    1. Daryl may be right but there is an unlimited number of such functions that, on solution, will give an unlimited number of solutions.
      In other words: you can pick an answer and construct a polynomial that will give you your chosen solution. That’s tantamount to cheating!

  8. Struggled with it for a few minutes and couldn’t get it, I even checked the web page, rather than the RSS feed, in case there was a corrected typo. Came back a couple of hours later and saw it straight away. I don’t understand how I missed it the first time round.

    1. This is a bit naughty. I had already got it, but I rather fancy your comment is too much of a spoiler.

      Of course, that may only be because I have already ‘got it’.

  9. About 10 seconds to realise there wasn’t a mathematical solution using the numbers as presented.

    Knowing from previous experience Richard can be quite crafty, I mentally changed my viewpoint and quickly arrived at the most probable solution (although it does break the symmetry of the provided numbers).

    So about half a minute in total – my quickest yet šŸ™‚

  10. To those who despair, put that frown upside-down.

    …. What? Did I say too much? šŸ˜‰

    Back on topic, it took me time to solve this. Someone in the comments said something about writing the above numbers down in a single column, and even then, it took a few minutes before it slowly dawned on me what was going on. Simply put, forget about mathematical formulas, you just need to step back and see things from a different angle.

    Also, writing the numbers down in the classic calculator style doesn’t hurt, either.

  11. Hmm. I’ve got an answer, not entirely happy with it, because it doesn’t quite look right, but it fits. I’ll have to wait for Monday.

    Took me about 5 mins, couldn’t see it straight away, so I did what I often do with these puzzles; walked away and when I came back I got it in about 30 seconds.

  12. I usually skip the math ones, but I stuck with this one long enough to see the trick. About a minute. Good one.

  13. Less than 10 seconds. It’s the sort of spin that some people notice immediately. On the other hand, why is the time important? As Professor I.M. Gelfand used to say, “you have to be fast only to catch fleas”.

  14. Finding it funny how so many people can’t resist showing off that they have the right answer by giving overly-obvious clues. Interesting. Glad I solved it before looking at any comments (about 10s).

  15. I got the principle in about 10 seconds, then struggled over the first character – in the end I had to write it down to “work out” the first character

  16. Nice puzzle, I solved it and it gave me some satisfaction.

    I’m annoyed by the way that so many people write down how long it took them to solve it. Surely the joy of these puzzles and problems is in working them out, not in solving them quickly or more quickly than others.

  17. Rufus: Richard invited people to let him know if they have solved it and how long it took them to complete the puzzle, now he also knows how many people didnt read the instructions.

    1. yeah, I saw that after I posted. Think it’s a bad idea. Is the motivation to do these puzzles in the ego-boost of solving them quickly or in the pleasure of solving them? Maybe people could comment on whether they enjoyed the puzzle and why.

      I enjoyed the challenge of this one, and the neatness of the answer.

  18. You guys are all crazy – it’s just a bunch of random numbers. Meaningless. I’m not falling for th

    Oh look! Look at that! Nice!
    In your face, world! Who’s the daddy?

  19. Wow! Very impressed with myself – saw it after about 15 seconds. I hardly ever solve them usually.especially when they’re number based.

  20. Took me about a min but was very simple – reminds me of whats it called… the thatcher effect? I think… Something along those lines

  21. Fun one! After following the Friday Puzzles for a bit, you know that you need to think outside the box to solve some of them. After reading the first couple of comments, I got it right away.,

  22. A terrific time Saturday night. We surprised my parents and they were thriled when they got there..Thank you! I used to be advised by the photo booth person that pictures would be online. Where are they?

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