A fun mathematical puzzle this week. 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?

As ever, please do NOT post your answers, but do say if you think you have solved the puzzle and how long it took. 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. Drew,
      You are in good company.
      Ricardo has made a typo in the second group.

    1. Paul
      I normally find these puzzles hard too, but you have given yourself a clue – “LOOK”

  1. 15 secs or so. I’m pretty sure I got it, but with these kinds of puzzles you’ll never know if you’re right until you see the answer.

  2. I did think I had seen something similar as soon as I saw the numbers in list one – and the numbers in the other two lists confirmed that hypothesis. So a matter of seconds, but a bit of checking required, and I’m still not certain it’s right if this is a “mathematical” puzzle in the true sense of the word.

  3. yes, done. Please – don’t call these ‘maths’ puzzles – it would make numerology and astrology sciences. This is an 11-plus type Verbal Reasoning / Kettell B style of puzzle (i.e. – NOT MATHS!)

  4. Is there meant to be the number 1 twice in the second group ? Or should the second occurrence be an 11? I still haven’t solved it, but that looks odd.

  5. Easy one. A few seconds. Calling it ‘mathematical’ is a bit of a red herring, but if you called it by a more appropriate name it looses the nuances of the very word ‘puzzle’.

  6. Bugger! Published my guess , can I delete? I thought this was an email, not a comment (small phone screen, but that’s no excuse). I just hope I got it wrong now.

  7. It took me no longer than just reading the question. I had an inkling at group 2, and confirmed it with group 3.

  8. It took me a couple of seconds.

    On a side note, I think I’ve been a programmer too long as my mind keeps wanting to change them to groups 0, 1, and 2.

  9. i saw this straight at once away. perhaps studying the stars helps me with seeing patterns.
    would be easier if given in roman numbers, ha ha.

  10. About half a minute to work out the rules for all three groups, after which it only took a few seconds to allocate 15, 16, and 17 to the relevant group (hint: there’s a clue in that although 5, 6 and 7 are in separate groups, 15, 16 and 17 all belong in the same group – together with 18 and 19).

    1. Richard asked ‘In which group…?’, (not ‘groups’), Implying the three numbers fit into the same group. So wrong wording again. Also, maths? I don’t think so. This is about as mathematical as sudoku.

  11. I agree with some of the comments above, as a maths puzzle this is a bit of a curveball. Solved in two boggles before I picked up a pen.

  12. Took me only .0045 seconds to reject this puzzle as too boring to solve, but luckily I have the previous one still on the front burner… let me see, two trains pass, one will take 4 hours to complete, the other will take 1 hr, dont use algebra, do it in the head, ….. zzzzzz (should last a good six months of entertainment at this rate)

  13. Took me about 15 seconds to realize what the third group was, and after that, 2-3 seconds to put each into its proper group.

  14. A way to make this actually a “mathematical” problem would be to show how the distribution amongst the groups changes as the integers increase. Anyone?

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