It’s the Friday Puzzle!



First, it would be great if you could spend 2 minutes taking part in my quick survey into sleep and dreaming.  All you need to do is click here.  Many thanks.

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.

Two friends are chatting:
John: How old are your children now?
Eric: None of your business
John: Oh come on, it’s for the Friday Puzzle.
Eric: Oh ok. Well, there are 3 of them, and if you multiply their ages together you get the number 36.
John: Can you give me more information?
Eric: OK, the sum of their ages is exactly the number of biscuits we just consumed.
John: That’s still not enough.
Eric: OK, my oldest child likes to watch the ‘Bets you always win’ videos on YouTube.
John: OK, now I have worked it out.
How old were each of Eric’s children?
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.

79 comments on “It’s the Friday Puzzle!

  1. Paul Rough says:

    What a strange conversation between 2 friends… lol

  2. Simon Taylor says:

    I got it quickly, but if the apostrophe is correct, I have probably got it wrong.

  3. ross says:

    That’s still not enough, I need more

  4. Navneeth says:

    “How old were each of John’s children?”

    I’m not sure if it’s part of the puzzle or a typo, but John never talks about his children.

  5. I bet John and Eric are kinky.

    • Anne Elk says:

      It *does* sound a bit like a weird kind of foreplay, doesn’t it?

      Anyway, I took a minute to solve the puzzle. Pencil and paper job. (And that’s not a further reference to foreplay either.)

  6. Anonymous says:

    less than a minute, most of which was finding a pencil

  7. Andrew says:

    No idea. And no idea how old Eric’s are either

  8. Non-Spoiler Alert says:

    I haven’t got a clue – 3 minutes

  9. David clark says:


  10. There are two possible answers as far as I can tell. Unless there’s some secret biscuit quantity information in there that I missed.

  11. ChrisR says:

    yep, reckon in about 1 minute – until Monday

  12. Anonymous says:

    Got it, similar to Professor & Assistant Problem

  13. Susqueda says:

    3 minutes. Knowing that a given information is not enough rules out most of the possibilites. Then there is not a great deal to do.

    • Alvin says:

      Ah, I see, I think. Because those two know how many biscuits they ate, even though we don’t?

      (Still don’t have the answer, but that helps).

  14. Stevie says:

    I didn’t find the puzzle at all difficult to understand and solved it fairly quickly.
    Reading through some of the comments, I wonder if there has been an edit or two to the original puzzle.

    • Geodetective says:

      The last three lines were different before he changed it:
      John: OK, my oldest child likes to watch the ‘Bet’s you always win’ videos on YouTube.
      Eric: OK, now I have worked it out.
      How old were each of John’s children?

  15. confused says:

    Are they names wrong towards the end or is that part of the puzzle??

  16. Eddie says:

    1, √35+i, √35-i

  17. The Masked Twit says:

    Unfortunately, having “solved” the first version of the puzzle, before Richard corrected the wording (the answer was “we don’t even know if John has any children”) I Googled to see what the original problem was and saw the answer, so I have no idea how long it would take me.
    Nice puzzle though.

  18. foolonthehill says:

    I’m definitely stumped by this one, and can’t get beyond 5 possible solutions.

    There are 6 factorisations I can do which solve Clue 1, only one of which is precluded by Clue 3. And Clue 2 gives me nothing. (Unless Clue 2 means “shared equally”, in which case I am left with 2 solutions).

    • foolonthehill says:

      (Sorry – I mean 8 factorisations of course, neither of which is mathematically excluded, but one of which I dismissed, and the other which is inferred as incorrect by Clue 3)

    • Geodetective says:

      I have the same problem.

    • foolonthehill says:

      Oops. Now I get it! I think I was confused by the original incorrect wording.

      Reading it again *in order*, there is of course a single well defined solution. A good puzzle after all!

    • Tom says:

      “Sum of the ages is not enough” is a clue, though.

    • Geodetective says:

      Oh, you mean John and Eric have been eating biscuits before chatting… I thought Eric and his kids had been eating biscuits… Ok… Yes, that is sufficient information.

  19. Solved. 2 minutes. I like these type of puzzles.

  20. Percy Veerance says:

    If John and Eric carry on eating biscuits at that rate they are not likely to see any of the children reach the age of 36.

  21. Steve Jones says:

    If the age is considered to be defined by the number of years only, then there are still two answers to this one, albeit that some might argue over whether the oldest would count as a child for one of the two solutions. He/she would still be one of the children of Eric, but the his last sentence indicates he still thinks of him/her as a child. That would leave one solution.

    Of course, if age is considered to include fractional years, it becomes insoluble, and it introduces tricky issues of how finely graduated age is defined in time.

    • foolonthehill says:

      For integer solutions, the puzzle *does* work to give a single answer only. The clues *in order* reduce the possibilities from 8 to 2 to 1. And it’s nothing to do with him “thinking” of the eldest one as a child

    • jh says:

      Two brothers can definitely have the same age (as an integer number of years since birth), and one being older than the other, even not being twins.
      That leaves two possible solutions.

    • Calgacus says:

      I came to the same conclusion. Two children with the same age, one will always be older than the other. There are two possible answers.

    • Steve Jones says:

      Actually, now I’ve bothered to do this properly, I seven “integer” solutions (after applying the relevant clues) of which I can eliminate 2 by introducing the constraint that somebody ceases to be a child at age 18. Of the five remaining, I can only reduce those two one solution by introducing two further conditions, neither of which are in, or implied, by the wording of the question.

      Now,if the wording of the final condition was “Eric: OK, my youngest child likes to watch the ‘Bets you always win’ videos on YouTube”, not “my eldest child”, then I can reduce it to just two solutions.

      I see somebody else has 5 possible answers. We’ll see on Monday.

    • Steve Jones says:

      oops – just seen it. Silly me.

  22. Lazy T says:

    Two mins to get a bunch of possibilities, four more to work it out.
    Were there any biscuits left over and if so please can I have one?

  23. liam says:

    Took me quite a while for it to click. I was too worried about the details I didn’t know.

  24. ctj says:

    there are two valid solutions.

    without explaining what is special about eric’s children, yes, parents of that kind of children really do think and talk that way.

    • Slow Learner says:

      As it is Monday now, so no spoiler problems, can you let us know what your two solutions are, ctj?

  25. Anne Nicklen says:

    Well I’ve got AN answer but wouldn’t like to have to prove its the definitive one!

  26. Mat says:

    A ha. I could see the point of the Eric’s last statement but not the point of the biscuits one – until I saw Alvin’s comment. I now have it. Cunning.

  27. Once I enumerated all the possibilites the answer jumped out at me… I made a stupid mistake in the enumeration process which meant I literally didn’t have the answer in front of me.

  28. Confused says:

    Without making assumptions about their appetites for biscuits, Eric’s age, Eric’s definition of “child”, or how old one has to be watch YouTube videos I get 7 possible solutions out of 8 total factorizations.

    • Confused says:

      I just now noticed the significance of the comment “That doesn’t help either.”

      Solved it in 8 hrs. 🙂

  29. Nick 666 says:

    Is this not incredibly easy or have I missed something-2 secs

    • Anne Elk says:

      I’ve been thinking along these lines for the last couple of hours, on and off. There must be something I’m missing. I’ll look forward to the answer.

    • ivan says:

      If you got it right, you should understand why most people are making heavy weather of it. If you think it is obvious to the average customer, you’ve got it wrong.

    • Ken Haley says:

      No way anyone could get this in 2 seconds, unless you either misunderstand the puzzle, or have seen it before. I HAVE seen it before, but it still took me a couple of minutes to solve it again in a way that I can explain to someone else. There is only one solution.

    • Averagely intelligent person says:

      I’m not so sure you are right Ken.
      Looking at the times people have claimed to solve puzzles in in past weeks, I think most of the posters on this thread would make Albert Einstein look like an idiot (I’m far too naive to think they might be exaggerating their logical or mental abilities).

  30. John says:

    After 3 minutes, I have a reasonable answer, can I get a biscuit ?

  31. Anita Dunne says:

    Took about 30 secs. And I am a maths drop-out!

  32. James says:

    As a parent of “those kinds of children”, I can attest that I definitely think of them in the manner that results in exactly one answer.

    Five minutes to work through the consequences of the second statement. Seconds for the rest.

  33. Gus Snarp says:

    For us Yanks, how many biscuits are in a tin? (You get them in a tin, right?)

  34. Hal Harris says:

    I got it in about 2 minutes, assuming Eric does not have children he doesn’t want to admit to.

  35. John says:

    Just letting you know, you switched who has the kids. At first it was Eric then you switched it to John.

  36. John says:

    Got it. That age of kid is a pain in the butt.

  37. Nick 666 says:

    Could one of the children be called Daniel?

  38. About half a minute. The usual method of simultaneous equations is not sufficient because there are 2 equations for 4 unknowns, but going off in another direction yields sufficient clues.

  39. Greg says:

    Well, I’m stumped. 7 possibilities from the first clue. Can eliminate one from the third clue. The second clue I can eliminate 3 options but only if I make an assumption about the clue which using think is right.

    • Greg says:

      Oh now I have it. Had to cheat and google the second clue for an answer. Very clever. Not what I was initially thinking.

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