Answer to the Friday Puzzle…..


On Friday I set this little puzzle…..I have come up with a way of sorting numbers into one of three groups. Here are some examples of the numbers in my three groups….

Group One: 0, 3, 6, 8, 9

Group Two: 1, 4, 7, 11, 14

Group Three: 2, 5, 10, 12, 13

In which group should I place the numbers 15, 16 and 17?

If you have not tried to solve it, have a go now. For everyone else the answer is after the break.

All of the numbers in Group 1 only have curves, all of those in Group 2 only have straight lines, and Group 3 have a mixture. So, 15 goes into Group 3, 16 into Group 3, and 17 into Group 2.

Did you solve it? Any other answers?

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 theiBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.


30 comments on “Answer to the Friday Puzzle…..

  1. kaggyxaggy says:

    17 in Group 1?

  2. Botalot says:

    Surely it depends on the font you’re using. That 7 looks as though it possesses a curve to me.

  3. Simon Taylor says:

    I don’t understand the answer, surely 17 goes into group 2?

  4. paulchelt says:

    17 in group 2 surely.

  5. Dave Rickey says:

    As others have mentioned, this depends too much on fonts to be a good puzzle (for example, on my computer viewed through Google Reader, 7 has a curve, and this page loaded directly gives 1 a slight curve on the top left). On the other hand, a font that used a digital-clock style for numbers would have nothing but straight lines.

  6. -M- says:

    Friday it said: “A fun mathematical puzzle this week.”
    This is not mathematical.

    Anyway, I didn’t get it.

  7. Skysland says:

    Yes, I thougt that I was wrong, because is very estrange answer! 🙂

  8. Slugsie says:

    Yup, exactly the answer I had.

  9. Tom Ruffles says:

    ‘Friday it said: “A fun mathematical puzzle this week.”
    This is not mathematical.’

    It’s called misdirection.

  10. Dharmaruci says:

    yes,yes, as Others have stated. on my computer the 7 has a curve. also on some computers the serif twiddles may have curves. not fair test. that’s why setting this puzzle in roman Numbers would be fairer.

  11. Lazy T says:

    got it, using recursive non-derivative algebra in a leveraged geometric configuration,
    They all were in group 2 on my calculator.

  12. Fabian says:

    I agree with -M-. I read this was a mathematical puzzle so I decided to dismiss any other patterns.

  13. Mickey D says:

    Yes solved it!

  14. Chris says:

    The question was misleading. You said “In which group” when you meant “groups”. Grrrr.

    • Eddie says:

      Not many others picked up on this except you and I. I was annoyed too.

    • The Masked Twit says:

      I noticed it actually, but did not comment. Richard isn’t very good at questions………
      on reflection he’s not very good at answers either.

  15. oddbodd13 says:

    I got it, as well as the fact that it had nowt to do with maths.

  16. I got it after one of the comments questioned the “mathematical” aspect of the puzzle alerting us all to revert to the old think out of the box cliche.

  17. says:

    I have defined a function f such that f(15)=0,3,6,8,9… ; f(16)=1,4,7,11,14… ; f(17)=2,5,10,12,13… . Unfortunately, this comment box is too small to write f in full.

    *This*, my friend, is a mathematical answer.

  18. Dormouse says:

    Blindingly obvious once it is pointed out. Embarrassing not to see it in a few seconds.
    Luckily I was still stuck on the two trains.

    • The Differently Sane Hatter says:

      Make sure you don’t make any unwarranted assumptions about ground and perpendiculars.

  19. Roxana says:

    i saw a really different pattern emerge. Usually when people start counting, they start at number 1 but this puzzle started on zero. Zero being the first number in the sequence, goes in group1. Then the number One, being the second number in the sequence, goes in group2. The number two is third so it goes in group3, and so on. that pattern continues until the number 8. 8 and 9 are in the first group (sequential numbers) and the numbers 12 and 13 are also sequential numbers and are in group3. After this, it’s complicated for me to explain . but there’s a bit more to it. Since we are dealing with numbers, one can think about them being group for many different reasons. Nonetheless, I do agree with previous comments, the original solution to the grouping wasn’t really mathematical.

  20. David says:

    Couldn’t get to grips with this but my 12 year old son spotted it in seconds – gutted!

  21. dave says:

    I didn’t solve it, because I’m lazy.
    But after reading the answer it made perfect sense.
    It is mathematical, if you look at the common factors in group 1 and 2 you would then be able to solve the problem. In it’s simplest form 1+2=3. JMO

  22. martin says:


    Did not make it explicit that 15,16,17 didn’t all go into the same group… Had me coming up with some crazy factorials

  23. Thomas says:

    I got it.
    What I don’t get is why the font sould be such a problem. When you learn to write numbers at school, you learn a standar way to draw them. So in my opinion even written in “corsiva”, 1, 7 and 4 are still known to be written with straigt lines.
    I understand better the messages that argue that this is not a mathematical puzzle. But couldn’t we consider that curves and straight lines are geometric matters, and therefore part of mathematics ?

  24. martin says:

    group vs groups…. WISEMAN!!!!!! *shakes fist*

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