# It’s the Friday puzzle!

99

Time 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 on “It’s the Friday puzzle!”

1. TS says:

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.

Forget the word problem, I want to know where three people can have dinner for only £25! 😉

• Niloo says:

I totally agree :))

3. Maybe at McDonald’s, but there’s no McWaiter…

4. Joanna says:

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)

• ScreamingGreenConure says:

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.

5. Michael K Gray says:

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

6. Stefan says:

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!

7. c00 says:

Yep, Know this one from the olden times. Though I heard it with three men renting a room in a hotel. I really like it anyway.

• Cas says:

I heard it that way too

• Bucket says:

moi aussi.

8. Frankie says:

Down the back of the chair with all the other loose change 😉 Yup, seen this one before 🙂

9. Marc says:

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…

10. Lucia says:

simply really! 😀

11. daveman says:

NULL problem. Just read it and thought one of these statements isn’t correct. Please post harder problems Richard Wiseman! 🙂

12. Zyaama says:

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. 🙂

• Vikram says:

i totally support entire youths spent having read comics!

13. Reggie says:

Hi,
That took about 2 minutes. Wrong entry keeping Mercantile Accounting rules. Cannot add the waiter tip.
Thanks

14. Actually I havent seen this one before! Also 3 people have dinner for £25?! That’s amazing!!

15. shpalman says:

I heard this one about 20 years ago, and I know the answer.

16. nikki says:

I haven’t seen this puzzle before, but think I’ve figured out the answer.

17. T9sus4 says:

Once I stopped thinking numbers and started thinking words, I had it. About 2 minutes, if that.

18. David W says:

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.

19. Erik R. says:

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?

20. Claudio says:

Ahoy! Shiver me timbers!

21. grthink says:

Apparently I’m the only person in the world not to have seen this before, but I’ve got an answer now.

22. Tortorific says:

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.

23. Nikodemus says:

A minute or so. Looking at where money really is at the end shows the trickery.

24. Tim Mills says:

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.

25. Tortorific says:

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.

26. Frank says:

I have seen this one many times, yet it still catches me every time. Dang. Eventually figured it out though.

27. Daniel Candido says:

This was so easy …
That I’m feared if I’m right!

• me says:

yep

28. Engywuck says:

Thats not really a puzzle!? Its a confusing presentation of a simple everyday thing…

29. Manfred Harlaar says:

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).

30. Kev says:

This one’s like a joke and relies a lot on the delivery. Doesn’t really work when it’s written down does.

31. Marvin says:

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.

32. Steve Bent says:

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!!

33. uksceptic says:

I’ve seen this before.

34. Ilijas says:

one of the guys has got the pound, no?

took a few seconds to work it out, but i remembered my days as waiter.

35. thornae says:

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?

• Aparna says:

Cowboy

• Tortorific says:

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

• Aparna says:

Great!

36. rhabarber says:

Hm, it took me 1 minute to figure out where the puzzle is…

37. Aparna says:

Its word’s play.

30 seconds

38. Pretty old puzzle, took no time to solve as i knew the answer 😉

39. Jerry Weaver says:

I remember this one from years ago. It’s not even a very good puzzle.

40. Travis says:

C’mon, Dr. Wiseman. This puzzle is older than you are. Are you running out of content?

41. Mark Probst says:

This is not a puzzle, it’s a non sequitur.

42. stephalump says:

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. ^_^

43. randOM says:

It’s always the same – I knew this riddle and have to start thinking it over again and again. But after few minutes I got it…

44. Veljko says:

Got me confused at first but after about a minute or so I came to grips with it. Not hard.

45. Nice Blog, liked it
Thanks for sharing

46. Mchl says:

Duh… Just worked on it yesterday… coincidence?

47. Gus Snarp says:

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?

48. Isabella says:

Maybe the £ got lost? xD Just joking!
Yeah I know that one too. A real classic.

49. Yura says:

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

50. Hugh Dixon says:

Do you think Gordon Brown could use this trick to balance the budget deficit?

51. Sam says:

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. 🙂

52. john randall says:

Classic example of “figures don’t lie, but liars can figure.
Simple misdirection

53. Skepdude says:

5 secs! Agree with Sam!

54. melissa says:

This is a good blog!

55. gry says:

i agree only 7 sec with Sam!:)

56. A few seconds – have heard this one before as tipping a busboy or paying for drinks as well.

57. Kayleigh says:

vat? 😀

I’m joking cos i don’t know the answer 😦

• ScreamingGreenConure says:

you can do it, just don’t let yourself get overwhelmed. Take it step by step.

58. Kayleigh says:

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!

59. Mike says:

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

60. 52X Max says:

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

61. ScreamingGreenConure says:

I don’t get it. I think I know the answer but I don’t understand the whole thing and basically why.

62. ScreamingGreenConure says:

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.

63. Mariama says:

Took me but a a minute or so to work it out. Thanks for posting

64. monoolho says:

Took me around 20 seconds after reading it. Never seen this one before, but some more complicated ones that have the same logic.

65. jane says:

I never heard of the puzzle.
Took me around a minute, including the reading

66. I’m American so when I see the pound symbol I draw a blank. Might as well be a in a foreign language. 🙂

67. spazzdog says:

14 seconds… a record for me as I truly suck at math.

68. Rex says:

ooh, took me a minute or so. I was right in not paying too much attention to the explanation included in the puzzle.

69. E Mon says:

I actually had not seen this before
iceswag

70. mustwriteit says:

it has gone nowhere because it did not exist.. miss calculation .. eh?

71. David says:

Embarrassing how many minutes it took me to figure it out. I gotta get out more! Thanks

72. kim says:

i remember this from years ago
but still can’t remember it
so i figured it out in 30 min tops xD

73. Niloo says:

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

74. Flavio says:

It took about 30 secs, that is if I got it right.

75. Jocelyn says:

stumbled across this blog… embarassed that it took me about 5min.

76. Ms G says:

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 … ).

77. Fabio says:

Can someone figure out this letter sequence and say which letter is missing?

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79. Danica says:

I’ve seen this puzzle so many times before but I’ve never figured it out :C

80. Danica says:

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? 😛

81. Kate Rawlins says:

Easy – you’ve gotten confused between Euro’s, Pounds Sterling, and Gold Standard US Dollars ! 🙂 / smiley face and thanks, Kate

82. phylliskirigin says:

Just got to approach it from a different perspective and forget the number 30.

• Danica says:

The funny thing is, the number 30 is never mentioned. We just read that there’s 3 guys and they gave 10 bucks each, and we assume 😛

83. maninalift says:

That is the most pathetic puzzle. It isn’t even a puzzle it just relies on the puzzlee not listening.

84. Sallybm says:

Yay! I got it straight away, was only confused for about a second. Feeling very smug and clever right now, ha ha ha 😀

85. Eva says:

Got it as I was reading the problem – my mind just kind of stuck at the “tricky” bit, so that’s how I figured it out.

86. i really like this one, if you think about it, its really confusing because to solve it create more puzzles, ahhhh. its really clever xxxxxx

87. Nobody says:

the waiter stole it

88. Bonnie says:

THE DRESS, IT’S GONNA BE HOT!