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. Mike says:

About 10 seconds – but only because something kind of similar passed across the radar a few days ago…

2. Drew says:

A few seconds. But only if I’ve got it right! Would like to test sice I can’t be sure.

1. Drew says:

Arghh – typo! I’ve lost all credibility now.

Drew,
You are in good company.
Ricardo has made a typo in the second group.
TNT

3. Murray P says:

Very good

4. All I have to do is LOOK at this one and know it’s one to pass up . . .

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

5. Niva says:

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.

6. Jimi says:

Took me about 10 secs to figure it out.

7. 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.

8. DAVE! says:

Took me 0.02154 seconds.
I’m so amazing.

1. Hugh Janus says:

Bother, I did it in 0.02155 seconds. I’ll get you next week pal!

2. Nanny Mouse says:

Snap! 0.02155 seconds. What are we like!

9. 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!)

1. You are so right. In fact, calling it a math puzzle threw me of the trail so I needed to read the comments to find the rule Richard presumably uses.

10. song bird. says:

?

11. Gib says:

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.

1. Gib says:

Apparently I was right, since Richard has now changed it…

12. Alex says:

Should that second 1 in group 2 be 11?

1. Alex says:

Never mind 🙂

13. 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’.

14. 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.

1. Looks like your guess got deleted, Pat. I don’t see it.

15. Walter says:

Took me exactly 33 seconds, which would go into group 1

16. pdurrant says:

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

17. AMWhy says:

I got it before I finished the question, but I love looking at numbers like that…

18. slugsie says:

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.

1. Jon says:

Interestingly enough, those would be more appropriate names for the groups.

19. Dharmaruci says:

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.

20. mittfh says:

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. slugsie says:

15, 16, and 17 do not all go in the same group.

2. Dharmaruci says:

15 16 and 17 do go in to the same group. my solution anyway.

3. slugsie says:

My solution has 15 and 16 together, but 17 elsewhere.

4. JohnDavid says:

I’m with slugsie on the 17 issue.

5. Eddie says:

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.

21. Lazy T says:

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.

22. deepfield says:

These puzzles usually take me three days to find the answer: until Monday morning, right here…

23. As Lazy T says, it’s a bit of a curveball, but I got it straightaway.

24. 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)

25. I saw this one immediately, I think. For a change! 🙂

26. I might not have gotten it without reading the comments. Richard’s term “mathematical puzzle” threw me. Richard, you devil, you.

1. Anon says:

Richard was once a professional magician. I think that the term is distraction.

27. As soon as I was about half-way reading the first of the three lists of numbers.

28. Chak says:

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.

29. Phil McCavity says:

Why is this called Friday puzzle? It’s Saturday

1. Phil McCracken says:

No its not, its Sunday!

30. Carl says:

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?

31. arrrgh, took a while to beat my math brain into submission and then look at this in a different light 🙂

32. Eddie says:

After a weekend puzzling over this one I think I’ve finally got it. It’s a bit black, white and grey.

33. Got it! Now to check whether it is the right answer!

34. Phroggie says:

Didn’t immediately spot the obvious, so it took about 30 seconds.

35. Duncan says:

I have a pretty good idea what the answer is, just don’t ask me to show my working…

36. Gail Hatton says:

too easy, pleeease give us something really difficult Richard, love maths