Please do NOT post your answer, but do say if you think you have solved the puzzle and how long it took. Solution on Monday.

Can you place six X’s on this noughts and crosses board without making three-in-a-row in any direction?

cross1

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.

92 comments

    1. A “naught” is the elementary particle of naughtiness. Sometimes written as “naughton”, pronounced, “Not on!”

    1. Something like that Lazy T.
      I don’t want to be too specific, in case my first answer is the official one.

  1. I would be interested to Chris’s proof of two solutions, because I have a proof that there is only one solution (treating rotations and reflections as equivalent).

    1. Shift your solution 1 square in any direction and you’ll find an other one 😉
      (if some of the x fall off the board, add them on the other side)

  2. About half a minute or so, brainpower only (imagining the positions rather than drawing them). I wonder how solutions there’d be for twelve Xs on a 4×4 grid / twenty Xs on a 5×5 grid?

  3. Maybe twenty seconds. It’s interesting that nobody’s chuntered about Dave’s spoiler. I guess readers have realised how easy it is to try solve the puzzle before looking at comments.

    1. 15 seconds or so. It’s even easier if you flip it to say “Can you play three O’s in a way which stops X making a winning line? OR I’ve got it horribly wrong and embarrassed myself on the Internet. And not for the first time…

    2. Brilliant, Janus. Thank you, as ever, for your laser-sharp one-liners. It would be a dark world without your wit.

    3. re first couple of comments – – it’s a noughts and crosses board – there are certain areas which are out of bounds 🙂
      and i do like the idea of the complementary problem with the 3 ‘O’s – that’s like playing the game and stopping your opponent from winning

  4. It took me 3 tries and about 15 seconds. I started intuitively, and when that failed the 2nd time, I went about it algorithmically, which worked right away. It’s a nice, easy puzzle which activates our puzzler just enough to feel accomplished, which brings down our guard for upcoming, more devious games.

  5. I love how every Friday there is a new puzzle posted and in the direction it says “Do not post the answer” but consistently, some twit within the first 0-20 comments has posted the solution. Takes all the fun out of it. Thanks Dave.

    1. I agree Bert.
      You are so right.
      We could practically be related.
      Do you have the same surname as me?

    2. It’s not fair!
      Bert started it!
      Besides, the Self Righteous Twats have a noble lineage and are one of the oldest families in the country.

  6. not too difficult. but as usual the wording allows a trivial non-solution solution. three xes slightly off center in each box makes them not align in a row. but even without such nonsense about 30 seconds

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