Main Page > Puzzles - Traditional-answer questions - self-referentiality

**Quiz - 50 good puzzles**

I am trying to amass 50 good puzzles! The scheme is that when I
find a new puzzle that is better than any of the ones below, I will replace
the worst one with it. Thus in theory this should evolve towards a super-cool
list of 50 puzzles... or at least, I'll think it's super-cool.

The 'Setter' column indicates who set me the problem, and
a '+' after their name indicates that they heard it from somewhere else. 'Class'
gives a rough guide to what type of problem it is, although some are left a
'mystery', since which type they are is half the puzzle. 'T-good' is how good
I (Tim) think that puzzle is - a '?' indicates a puzzle I haven't solved (and
hence can't really judge). The ratings are out of 10 and the one at the bottom
of the list will probably disappear on the next update. The 'L' column gives
a 1 for the puzzles Laurence has solved, a 0 for those he hasn't and a n/a for
those he doesn't particularly want to solve.

# |
Description |
Setter |
Class |
Difficulty |
T-good |
L |

1 | [e,f,n,o,s,t] or [E,F,N,O,S,T] what property to these letters share? | Michael | ? | ? | ? | 0 |

2 | What is unique in English to the letter 't', only true of 'h' and 'v' in French, and not true for any letters in German? | Michael | language | ? | ? | n/a |

3 | INCoNSiSTeNCY, BeAr, WAtEr, PHIAl... all ok. But pHIAl, noooo! And Candle is impossible... what?!? why?? | Michael+ | ? | ? | ? | 0 |

4 | 6, 5, 3, 9, 8, ? | Nick's revenge | ? | ? | ? | 0 |

5 | Who led the pedant's revolt? Which Tyler!! Geddit? | Michael+ | geddit | ? | ? | ? |

6 | If there are 3 people in a room, what is the probability that at least 2 of them are of the same sex? | Ross+, from guy+ in computer room) | probability | 1 minute | 10 | 1 |

7 | Given that women are pregnant for nine
months and that men can refertilise within a much shorter space of time,
it would seem that to maximise our reproductive capability as a species,
the percentage of females should be more like 95%. In fact, the percentage
is about 50%, as we know. So why is the optimum percentage 50% and not 95%
as one might naively expect? (Note - this isn't simply because men have an X-chromosome and a Y-chromosome. The number of sperm manufactured with each different chromosome can be controlled, and thus evolution can (and has) guide us to the optimal percentage - which is in fact about 51%). |
Tim | probability | 1 week | 10 | n/a |

8 | An island, visited daily by a boat, is inhabited by 100 people, all with red eyes. Bizzarely, having red eyes is in fact a terrible social taboo, and anyone who finds out that they have red eyes will immediately leave on the next boat through shame. But no-one can see their own eyes, there are no reflective surfaces. And it is such a taboo that they will not even say to another of their tribe, 'you have red eyes! Aaaaagh!' or something. One day a visitor comes. As he is leaving, and the whole tribe (presumably) is bidding him farewell from within hearing distance, he shouts, "At least one of you has red eyes!" so what happens next!? | Michael+ | logic | 1 month | 10 | 1 |

9 | But... surely they all already knew that at least one of them had red eyes? So why should saying that make any difference? | Tarim, then others | logic | 1 month | 10 | 0 |

10 | There are twelve wires that run from your cellar to your roof. Unfortunately on their journey they could be randomly mixed up, so you can't tell which cellar wire-end corresponds to which roof wire-end. You have a battery and a light bulb, and you can temporarily twist wires together. You can also travel from the cellar to the roof and back again any number of times. Thus you can construct circuits and test the wires at either end in order to deduce what is going on. But it’s a long way to the roof. So, starting at the bottom, what is the minimum number of journeys you have to make, in order to work out exactly which wire-end in the cellar corresponds with which wire-end on the roof? | Michael+ | logic | 1 month | 10 | 1 |

11 | Why do you always find things in the last place you look? | famous+ | lateral | 1 minute | 10 | 1 |

12 | A rickety bridge must be crossed in the dark! Only two people may cross at once. Four people must cross. They have one torch between them which is vital to make a crossing. The torch only has 17 minutes of batteries left. The people all take different amounts of time to cross the bridge: one takes 1 minute, another takes 2, another 5 and the last 10 minutes to cross. So how can they make it across without getting more batteries or any other such silliness? | Nick+ | logic | 15 minutes | 9 | 1 |

13 | (0,1):(18,19):(28,29):(38,39):(79,80):(?,?) | Tim | mystery | 1 week | 9 | 0 |

14 | 2, 4, 6, 32, 34, 36, 42, 44, 46, 52, 54, 56, 62, 64, 66, ? | Tarim+ | mystery | 1 hour | 9 | 0 |

15 | In a non-gravity environment, how many cubes of the same size can be arranged around another cube such that they all have at least one surface in contact with the centre-cube's surface? | Michael(+?) | spatial | 15 minutes | 8 | 0 |

16 | The following words share a property: Almost, Biopsy, Chintz. Can you find a number with that property? | Michael+ | mystery | 1 week | 8 | 0 |

17 | A bicycle stands freely (somehow). The pedals are in their highest and lowest positions. If you push the lower pedal backwards (i.e. in the direction the bike is not facing), which way does the bike go? | Tom+ | physics | 1 week | 8 | ? |

18 | A rod is attached to the floor of a train by a flexible joint. The train goes on an arbitrary journey: is it possible to start the rod in a certain position such that it doesn't hit the floor of the train for the entire duration of the journey? | Michael+ | physics | 1 week | 8 | ? |

19 | Which way up does an iceberg (2D) float if it is shaped like a quite pointy triangle | Tim | physics | 1 week | 8 | 0 |

20 | Women seem to be more popular than men, if magazine covers are anything to go by. Assuming that everyone will keep having babies until they get a baby girl, but the most anyone can have is five babies, which will there be more of - boys or girls? (assume the chances of having a baby girl are exactly 50%) | Tim | probability | 1 hour | 8 | 0 |

21 | When is 1 and 1 not 2? | Tim | lateral | 15 minutes | 8 | 0 |

22 | A young girl says: "I'll clap a song, and you have to guess what it is. Ready?" and claps as follows: 'clap, clap, clap, clap, clap, clap, clap, *pause*, clap, clap, clap, clap, clap, clap, clap'. She then offers the clue, "It's to do with lettuce." What is the song? | Young Girl on a train | lateral | 5 minutes | 8 | 0 |

23 | Zeno, William the Conqueror, Henry the Eighth, Jean Fourier, Franklin Roosevelt, Louis XIV, Severus Snape, Pliny the Younger, Pliny the Younger, ? | Tim | language | 15 minutes | 7 | 1 |

24 | Two climbers were climbing roped together in the Scottish Highlands. They saw some eagles soaring above them. Later the climbers slipped over the edge of a precipice and unfortunately plunged to their deaths. Their souls left their mortal bodies and ascended to heaven. As they rose they saw the same eagles and one soul cried out to them, 'Ah - Eagles!' But the eagles, being polite, said nothing. geddit? | Dan+ | geddit | 1 week | 7 | 0 |

25 | With two fuses of indecipherable thickness but both known to burn for exactly 1 hour, and a box of matches, how might one time 45 minutes? | Radio program+ via Will, and more recently Tom+ | logic | 15 minutes | 7 | 0 |

26 | Alright then, how about if you only have one of those fuses, how are you going to time 45 minutes now?!? | Tim | lateral | 1 hour | 7 | 0 |

27 | How are you even going to make a fuse of random thickness that you know will burn for exactly one hour anyway? | Tim | lateral | 1 hour | 7 | 0 |

28 | If Green is Blue, Blue is Green, Red is Yellow and Yellow is Indigo, what is Indigo? | Tim | mystery | 15 minutes | 7 | 0 |

29 | person, fiddle, degree, estate, column, sense, ?, ... | Michael | mystery | 15 minutes | 7 | 0 |

30 | If C stands for a consonant and V for a vowel, what does this say: "CVCCVCVCVC CVCVV"? | Weekly newspaper puzzle thing | language | 5 minutes | 7 | 0 |

31 | What word is an anagram of itself? | Michael | lateral | 5 minutes | 7 | 1 |

32 | E, S, S, F, F, T, T, E, ? | Tim and Nick | mystery | 15 minutes | 7 | 0 |

33 | Same letters and ordering in each gap: A _ _ _ _ _ _ _ surgeon was _ _ _ _ _ _ _ to operate because he had _ _ _ _ _ _ _! [NOT 'PREPARED'] | Dan+ | language | 1 hour | 6 | 0 |

34 | At ----- do not tell me the ----- ----- of the ----- which ----- -----. Same group of five letters in each gap. | Michael+ | language | 15 minutes | 6 | 0 |

35 | explain/continue the series: M on a line, heart on a line, figure 8, M with a line through the middle horizontally, apple on a branch, bunch of cherries, triangle | Michael+ and a book+ in Tim's past | mystery | 15 minutes | 6 | 1 |

36 | Find as many and as long as possible names of animals [strictly, names of species, in English, but bending rules is always fun too] without using any of the letters M to Z. | Tim | language | 15 minutes | 6 | n/a |

37 | Do it again but don't use A to L! | Tim | language | 15 minutes | 5 | n/a |

38 | Given 10 bags of gold coins, and knowing that one bag contains only fools gold (which weighs less), how can you find out which coins are fools gold with just one weighing? (you know how much both weigh) | Matt+, and ancient maths poster+ | logic | 1 hour | 6 | 0 |

39 | You have a straight chain consisting of 7 links. You have to pay to stay at a hotel for 7 nights, paying 1 chain link for each night as you go. What is the fewest number of breaks you need to make in the chain? | ancient maths poster+ | logic | 15 minutes | 6 | 1 |

40 | What is the longest chain/number of nights staying you can do that with if you are allowed one extra break than you just used? | Tim | logic | 5 minutes | 5 | 0 |

41 | 1, 21, 21000, ? | Tarim | mystery | 15 minutes | 6 | 1 |

42 | My ________ is _________ than my wallet. put one word in both gaps? [NOT STILLER] | Nick+ | language | 15 minutes | 5 | 0 |

43 | 10, 10, 10, 12, ? | Nick | mystery | 5 minutes | 5 | 0 |

44 | Kangeroo words contain a synonym within themselves, in the correct order. Find the synonyms for: Notice. Appropriate. Separate. Calumnies. Position. Falsities. Apposite. | Michael+ | language | 5 minutes | 5 | 1 |

45 | 1, 15, 6, 19, 14, ? | Tim | mystery | 15 minutes | 5 | 0 |

46 | Think of words that end in -gry. Angry and Hungry are two of them. There are three words in the English language. Can you think of the third one? It is a common word that everyone uses every day... | famous+ (often mis-stated such that it is unsolvable!) | mystery | 15 minutes | 5 | 0 |

47 | Define the letters of the alphabet using self-referential common phrases (e.g., "first of all" defines "a"). | rec.puzzles+ | language | 1 month | 5 | 0 |

48 | You know there are 3 black hats and 2 white hats. You cannot see your own hat. The challenge is to work out what colour it is. You and two others (perfect logicians) each have one of the 5 hats. You can all see what colour hats the others are wearing, but not your own. Everyone wants to be the first to work out the colour of their own hat. You can see one of them is wearing a black hat and the other a white hat. How can you tell what colour yours is? | Mr. Crisp+ | logic | 5 minutes | 4 | 1 |

49 | Continue the sequence: ..., autumn, journey, psychic, acquaint, borrow, assail, thatch, ? | Tim | mystery | 15 minutes | 4 | 0 |

50 | You can fit 100 unit squares into a 10 by 10 area. How many can you fit in a 10.5 by 10.5 area? | Laurence+ | unsolved research problem | unsolved | 4 | n/a |

Laurence has a nice selection of 'Stripper puzzles' - puzzles that all involve a stripper. (It was going to be puzzles that involve a farmer, but I suggested that a stripper would make it more popular).

Here are some puzzles which are not in the top 50, and were either considered for it or knocked out by other puzzles I considered more worthy. The last column briefly indicates what rules it out from the top 50. Note this will now include puzzles I have not yet solved, since I can't really judge if they should be in the top 50 or not.

# |
Description |
Setter |
Class |
Difficulty |
T-good |
L |
Why not? |

1 | 1, 1, 2, 7, 18, ? | Nick | ? | ? | ? | 0 | Nick doesn't know the answer... |

2 | Odd one out: 15, 17, 19, 21, 25, 27 | Laurence | ? | ? | ? | 1 | Unsolved by Tim |

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