tipping-759828_FullTime for another classic….

Three men go to a restaurant for dinner and spent £25. Each man gives the waiter £10. The waiter keeps £2 as a tip and gives £1 back to each man. Thus each man pays £9, and so the group pay £9 x 3 = £27. The waiter keeps £2, making a total of £29. So, where did the missing £ go?

The answer to this puzzle, and 100 others,  can be found in a new kindle ebook called PUZZLED, and is available in the UK here and USA here.

99 comments

  1. Have my life come full circle and there is only age old puzzles left to solve?

    Remember this from way back before the internet was widely available and people had to solve such things rather than googling it.
    It took me a couple of days to get to grips with this one.

  2. I want to know if there’s anyone who *hasn’t* seen this puzzle before.

    Also, isn’t £2 a pretty crappy tip?

    @ButMadNNW: I can get a decently large plate of pasta for AUD$15 (a little under £8)

    1. I haven’t seen it before. I haven’t seen most of the puzzles posted here, I only started trying them out when I saw them posted on this blog.

  3. I took around 10 seconds to confirm that I had accurately remembered this puzzle from years ago.
    It relies on conflating debit with credits…

  4. I had never heard this puzzle before but it tooks me like 2 minutes to figure out. Sorry. I guess you can’t fool a programmer with this kind of stuff. 🙂

    But hey, it was fun!

  5. Hmm. I think I might have come across it before, but if so had completely forgotten the details.
    In any case, looking over it now, I don’t see a puzzle at all.
    It’s just a trick in how it is presented…

  6. I actually had not seen this before. Guess spending a youth reading comic books instead of puzzles has to pay off some time. Still, seeing the problem took me about the time it took me to finish reading the question.

    Too easy. 🙂

  7. Oh man, this takes me back.

    This one really troubled me aged somewhere between seven and ten. I got stumped three or four times over the course of several years, as I repeatedly would forget about it then read it in some book or hear it from a friend. No one would (or could) explain it to me.

    Then when I was in my teens I came across it once more, thought “Hang on a minute…!” and the problem was solved.

    Talk about rewarding! I’m kinda glad there was no internet back then. I really had to fight for the answer (inconsequential as it may be) and the satisfaction was utter.

    David

    P.S. to those who just see a question posed incorrectly: that’s all any of these puzzles are. It’s just that some catch us, some don’t, and we’re all different as to which does which.

  8. I figured it out! The answer is that it should be “to a bar for a single drink each” rather than “to a restaurant for dinner”.

    We’re supposed to be solving what sounds wrong with this story, right?

  9. The thing that always cracks me up about this puzzle is the way people attempt to explain the answer. It’s one of those blatantly obvious puzzles that use a little bit of verbal trickery so you don’t notice the answer but I’ve heard even other people in the mathematical field get confused explaining it.

  10. I vaguely remember this puzzle. Still, it took me a minute to come to the answer. Thanks for sharing it, Richard – it’s good to remember that there are very obvious ways we can be fooled, as well as clever and subtle ways.

  11. In an unrelated question about a twitter post from Dr Wiseman:
    How to detect a liar from their handwriting http://tiny.cc/2aEul
    Aside from the headline and the first few sentences this is a well written article. I’m Australian so I haven’t come across the daily mail before are they usually good with science or did you have to slap them repeatedly? It’s hard to find half decent science news but the other stories on their site seem not horrendously bad.

  12. It is like the trick with fingers:
    Your thumb on your left hand is ten, the next finger nine, the next eight, the next tot that seven en the littlest finger is six. Then substract the five of your right hand and that leaves you with one missing finger (6-5=1).

  13. Haven’t seen this before. Thought I had it twice before getting the actual answer. Now it does seem obvious. At first you just picture the events unfolding linearly and might be fooled by the description.

  14. This took me way longer than it should, 2 seconds once I got a pen, after only jotting down 2 numbers the answer slapped me in the face.

    …and I think I’ve seen this before in my youth….

    Poor effort from me…eh…7th day at work on the trot including some travelling and soem very early starts….

    That’s my excuse!!

  15. Okay, here’s a similar problem which I found in an old book of puzzles (including the above Friday puzzle).

    There are two adjacent countries – let’s call them Brainada and Puzzlekia. In Brainada, the Puzzlekian dollar is worth 90 Brainadian cents. In Puzzlekia, the reverse is true.

    So, there’s a place on the border between these two countries where there’s a pub on each side, within walking distance. (And I’m sick of typing “Brainada,” so we’ll now refer to them as B and P.)

    A thirsy cowboy goes into the pub on the B side with one B dollar, and orders a ten cent beer (it was a *really* old book). He gets his beer, drinks it, pays, and asks for his change in P dollars. Since his change is 90 B cents, the barman gives him one P dollar.
    The cowboy then walks across the border to the P pub, and repeats the process. Ten cent beer, change in B currency = one B dollar.

    He walks back and forth ten times before his thirst is quenched. At the end of this, the P and B bars both have 50 cents more of their respective currencies, for the five ten cent beers each sold.

    The cowboy is back to having the one B dollar that he started with.

    Who paid for the drinks?

    1. The bars gave the beer away. He gives the bar a dollar and gets back a dollar in the other currency the other 90 cents isn’t important the net result is he is paying 10 cents in one currency and getting 10 cents back in the other currency per beer; though the bars are up 50 cents in their own currencies they are down 50 cents in the other currency.

      For the conversion rates to hold both currencies must be worthless.

      Realistically one or both of the bars is undervaluing the other’s currency (i.e. the true conversion rate is higher) and that bars is the one paying for the beer.

      Here is the maths part:
      you have two simultaneous equations
      B=0.9P
      P=0.9B
      substitute P
      B=.81B
      .19B=0
      B=0
      substitute B
      P=0.9×0
      P=0
      therefore P=0, B=0

  16. lol, It’s cute but not that hard. Took me about a minute and a half and I took out my pen and paper to puzzle it out just before I got it. ^_^

  17. Well I never saw it before. Working backwards it was easy to see that there was no disappearing money, but I did enjoy working through it to find the error. I think these three guys worked for ENRON. Does that joke play in the UK?

  18. I had to draw a diagram…= =;; but I figured it out
    I’m a math major too…ugh / _ \ need to sharpen up my skills!
    but it was fun hehe

  19. This one was easy, a few seconds to get – just follow the logic and the answer’s pretty obvious.
    I think it works better when spoken, as it’s harder to follow that way. 🙂

  20. ok i get it now, but does this even count as a puzzle? If you add it all up as you go along you get the right answer, it’s only the bit near the end that tries to mislead you. It’s sneaky, that’s what it is!

  21. I knew this one as a hotel room, and it still confuses me. Seems like something accounting and insurance people put to use a little too much before the recession started. Funny math … lol

  22. I think Richard just wants us to sit back and relax, and then, when our brains are all rusty from lack of using he’ll come up with a really hard puzzle…

    that’s my theory, anyway, cause this took less than 2 seconds to solve

  23. you guys are really ungrateful sometimes, though. Why are you always complaining when a puzzle gets posted here? It’s either too easy or doesn’t make sense, judging from the comments every week. Poor guy might get annoyed and stop posting them at all.

  24. I’m following ur post recently, and it was the second time I could solve ur puzzles
    feels good:D
    btw it took almost 30 seconds to figure out

  25. Ehehehe …. why the comment button then … huh? It did not take me that long at all, also due to my absolutely nonsubmissive state (what the hell is he babbling about there … let me check/build this my self .. the numbers … ).

  26. Haha, I just figured it out now. It’s the wording that puts you off, because how come suddenly they’ve paid 3×9=27 for a meal that cost ’em a total of 25? 😛

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