John has a problem.  He has been handed 7 pebbles by a friend and told that he has to arrange them so that there are 6 straight lines of pebbles, with each line containing 3 pebbles.

If John cannot solve the puzzle then his friend will murder him.

Can you help prevent John being murdered?

As ever, please do NOT post your solution, but do feel free to say if you have solved it and how long it took.  Answer on Monday.

97 comments

  1. Well spent the first few minutes fussing over the fact that we haven’t had to kill anyone or have anyone die in weeks and then here he goes again……man with “friends” like this poor guy who the heck needs enemies…..then took a few seconds to think the answer and about a few more to find paper and then draw it out…..so about one to one and a half minutes.

    1. And now I think I’ve probably got the intended solution. It’s an extension of my 2nd solution. (As for my 1st solution, it’s debatable whether or not it’s valid.)

    1. … of course … if he’s threatening you with death you could always put the pebbles in a sock and hit him over the head with them so he can see stars in lines then leg it while he’s unconscious!!

    1. That was my thought too. Maybe John is a really unappealing guy, if this is what he calls a friend.

  2. This so-called friend seems to get mighty angry about trivial things. Lay three pebbles out in a long line that leads to a padded cell and professional help. Once he’s safely contained then demonstrate the solution.

    1. I think this would be 35 line segments, not 35 lines.

      My solution that uses three pebbles and provides an infinite number of lines is perfectly fine, however. 🙂

  3. Wow, that’s a pretty dire consequence for failure. But I guess I’ll get murdered in my sleep because it’s past midnight here in the US and none of my ideas quite work.

    1. I did come up with a bunch of 5-line solutions, though, and one that could arguably be considered 35 lines (probably the same as Ed’s) but that just seems too cheap and obvious.

  4. I did my bit to help by phoning the police and telling them of John’s “friend”‘s nasty threat. They’ll be beating down the door any minute to rescue him.

  5. A few minutes. Most of those spent pondering the “friend” issue. Why the need for violence? Whatever happened to simple bets for a pint? (A little voice tells me that this was the real meaning of the Friday puzzle. Let’s not forget the whole psychology thing here…)

  6. Easy. The question is not about how to arrange the pebbles, but how to prevent John beng murdered.

    Throw the pebbles at the friend’s head one by one. With 7 tries, the accuracy will improve and eventually incapacitate (or even kill) the friend. A clear case of self-defence.

    Of course, if you wish to arrange the 7 pebbles in 6 rows of 3, that is also quite easy – a minute or two to solve.

    1. Oh, by the way, my name is really John, so I have a bit of a vested interest in this one, as I do not wish to be murdered!

  7. I instantly got the solution with 35 lines of 3 pebbles, probably the same as FEDragon’s “trivial solution”. Since 35 is 7C3, that is the maximum number of lines possible.

    Took a couple of minutes to get a solution with 6 and only 6 lines of 3 pebbles. One can actually deform the angles to any value between 0 and 180 and the lines remain straight, so in one sense it is just one of an infinite class of solutions. Modulo those deformations, I expect it is unique, if the method of generating multiple lines in the “trivial solution” is disallowed.

    1. What I called the trivial solution is a possible loophole in the wording of the puzzle, and there’s a good counterargument that it isn’t valid and the puzzle is worded quite adequately. A sufficiently well-paid lawyer, however, could argue otherwise.

  8. I’m intrigued by how many of you are getting six lines (or even thirty five lines) – I can only get numerous variations on a theme of five lines, assuming we’re talking a 2D space and the lines don’t have any kinks in them.

    Even laying them out straight, surely that would count as one line of seven pebbles rather than five lines of three?

    1. 35 is probably the number of combinations of 7 pebbles, 3 by 3… obviously, they are thinking on 7 pebbles in a straight line. I agree, that’s cheating, and likely, a violation of the definition, “lines containing 3 pebbles” (even assuming that by that, is intended a segment of a line… which is a assumption I don’t like): only 5, as you said, contain 3 pebbles, all the others will have more.

      But is quite possible to have 6 lines in the spirit of the problem.

  9. LOVE the heightened jeopardy in this week’s puzzle. I hope you guys have the answer right. For John’s sake.

  10. I quite like this one. I don’t’ normally dig the geometric ones too much, but this one seemed to flow quite logically and, after a bit of thought, the only reasonable solution seemed to magically present itself to me.

    Less than 5 minutes.

  11. Sure. Get a slingshot and and hit that sucker in the head with his pebbles.

    As for the geometric problem: easy

  12. I liked this one. Tried it for a few minutes, couldn’t get more than 5 lines. Then an hour later, I glanced at my drawings, and it hit me in a flash.

  13. I have a method of laying out 7 pebbles which results in 35 straight lines of 3 pebbles.

    Of course, the problem is not to provide this, but to stop the fellow being murdered. An entirely different proposition.

  14. I was able to solve after thinking for a few minutes and verifying in drawing software.

    And there was no ‘cheating’ involved. No curves, and my solution contains exactly 6 lines of 3, no more and no less. There is no other way to describe the arrangement except as 6 lines of three (except when you describe more complex shapes). What I mean by that is there are no 4-stone lines, etc.

    1. @Matt last week everyone was getting the answer in seconds and I mean everyone…..I thought I was going to have to hide under my bed and never face the world again as I didn’t get the answer until 20 looooooong minutes later, but don’t let it bug you really. Don’t lose the fun that is the Friday Puzzle! Just wait til Monday and see who really got what and when…lol…now that just as much fun!

  15. Another quick to solve puzzle. Helped that, by chance as I read this, I had seven coins in front of me. Unsure if I’d haver been as quick if I’d mentally moved things. Probably, but I’ll never know…

  16. My first solution is to phone the police and having the friend arrested.

    Other than that I’m only getting 5 lines. My excuse is a banging sore head so will let it subside and try again tomorrow.

  17. First time I looked at it I was stumped, but once I visualised putting 6 pebbles down on a flat surface, it clicked. Seconds, the second time. Minutes to give up first time around.

  18. Got it in about 10 minutes. Or “eventually”, as it’s also know.

    (I also tried using extra dimensions but that resulted in a solution where I went back in time; luckily this allowed me to call for help before my “friend” set the problem. Oh and for some reason I was wearing a Fez) 😛

  19. Presumably a pebble splitting in two as it hits the “friend” in the head, so forming 6 2/2 pebbles would be considered cheating? 🙂

    1. if said “friend” lives…..yes it would be cheating…
      if said “friend” dies… not cheating and everyone lives happily ever after…. or until next Friday…. :}

  20. For those of you still not able to get this puzzle, here’s a hint: The middle stone of each line needn’t bisect the line segment. In fact, the middle stone of each line bisects only half the lines formed by the intended solution.

  21. It’s been over a day and I’m still stumped… 7 coins on the desk aren’t helping. Going to spend them on something LESS FRUSTRATING!!! 😉

  22. I mentioned the problem to an online friend, who said he’d found two solutions. One pointed the way, and the other was definitely not square, hexagonal or even a heptagon.

    Of course, mentioning the solution shapes themselves would be a bit of a giveaway, so I haven’t – but you may be able to infer them from my previous paragraph 🙂

  23. Applause for all those who solved this puzzle withing the minute or so. It took me 90 minutes of thinking and drawing an a good nights sleep. This morning it stroke me. I made one drawing to check the possible solution. It fits, so I consider this the correct solution with exact six straight lines. All other solutions (3, 4 10, or 35 lines) crossed my drawing board but exact six was hard.

  24. I’ve got an answer that might be the right one, but I’d question the definition of ‘straight lines’. If John’s friend accepted my answer, I’d advise John to murder him for asking such a dodgy question

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