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Some doctors and a lot of hand shakes

At a congress there are some doctors, and everyone shakes a certain number of hands (never more than once with the same person). The doctors can be divided in two groups: -Group O: the doctors who ...
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  • 165
1 vote
1 answer
54 views

Triple up, pair off, and single out

Can you transform this word triple PELTS SORES DIVAN into this word triple PLOTS DIVES SANER just by swapping pairs of ...
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  • 10.4k
1 vote
2 answers
73 views

Fastest way to helpmate

What is the fastest way to checkmate/helpmate white(A helpmate is a type of chess problem in which both sides cooperate in order to achieve the goal of checkmating Black/White) in this given position? ...
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-1 votes
0 answers
41 views

Number Riddle - to words

New here but working on a number riddle and searching for methods led me to this site on a former riddle. Which word answers this riddle of numbers? The riddle is below. 2058 48104515819 307 35548418 ...
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1 vote
0 answers
51 views

How do I solve this six-piece Burr puzzle that becomes a knot?

I've seen a few solutions to this problem on the site, but none of the pieces used in those solutions have the exact shape as the pieces I have. This isn't the exact puzzle, so the colors do not ...
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2 votes
1 answer
65 views

Feeding Time at the Zoo - It's Common Sense!

Azeez the Assistant Zookeeper shook his head - "I'll never remember this" "Nonsense!" snorted Jeff. "It's common sense... no two animals eat exactly the same meals and for ...
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2 votes
0 answers
92 views

The first or last

CF CA AH AJ BA AG CF CA CH CJ AG
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  • 13.9k
0 votes
0 answers
90 views

We are part of the equation too [closed]

What does this weird equation relate to in the picture? How can we make sense of the equation and rights now?
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22 votes
3 answers
1k views

I got ninety-nine problems - so here's another one!

To date, on Puzzling.SE I have contributed (counting: 10, 20, 30...) 99 problems to the site. So to mark my 100th, here's a massive meta-puzzle to celebrate the occasion! Task Solve the nine sub-...
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  • 94k
12 votes
2 answers
758 views

Colour in a 5 by 5 grid, with evolution rules, so that the starting grid is the same as the output grid

Colour in a 5 by 5 grid using the colours Red, Blue, Green and Yellow. Each cell is considered to have 4 neighbours (to the left, right, above and below.) The grid wraps, so e.g. the top right is a ...
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  • 143
0 votes
1 answer
116 views

Will Romeo meet Juliet? [duplicate]

Romeo and Juliet try to meet each other everyday at a certain place between 12:00 and 13:00. They arrive at the place at a random time between 12:00 and 13:00 and they wait 15 minutes (but never after ...
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  • 165
0 votes
1 answer
66 views

How many colleagues went to Starbucks?

You go to Starbucks with some colleagues, everybody gets a cappuccino. Every cappuccino contains only coffee and milk (at least some coffee and some milk) and no other ingredients, but everyone has a ...
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  • 165
8 votes
1 answer
570 views

You have my sword – A signed letter from Gladys

Letters from Gladys are geography-themed standalone crosswords. Each puzzle has five thematic answers, which are places, sights or landmarks in or around a certain location (in this case, an ...
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  • 67.4k
0 votes
1 answer
69 views

A barrel contains 10l of whiskey, another one contains 10l of coca-cola. If I do the following operation [duplicate]

A barrel contains 10l of whiskey, another one contains 10l of coca-cola. If I do the following operation in two steps: 1 step) with a glass I transfer 200ml of whiskey from the first barrel to the ...
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  • 165
12 votes
1 answer
924 views

Patrick and Rachel go to a tennis tournament with 7 other couples

Patrick and Rachel go to a tennis tournament with 7 other couples. Each round is a single's match (1 vs 1). Nobody plays against his/her partner and nobody plays twice against the same player. At the ...
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  • 165
0 votes
0 answers
44 views

Disguising a Rubik's Cube rotation

I'm wondering if there's a way to disguise the total rotation of a Rubik's Cube? For example, if I wanted to rotate the (solved) cube I could obviously just apply a 90 degree yaw rotation. However, I ...
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-2 votes
1 answer
157 views

Sum of digits of numbers

Let S be a function such that S(N) is the sum of digits of N. N belongs to natural numbers, and N < 10²³. N does not contain a zero digit in it. The numbers are in base 10. Find the number of N ...
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3 votes
1 answer
132 views

Tiling twelve 5 x 10 rectangles with ten sets of the twelve pentominoes

I have ten copies of each of the twelve pentominoes. Can I use all of them to completely tile twelve 5 x 10 rectangles?
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-4 votes
0 answers
52 views

How to solve a 4x4 pyraminx? [closed]

How do I solve a 4 by 4 pyramix? Please include parity Please help
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  • 1
-2 votes
2 answers
106 views

FIND 4 sets of 5-letter words using these non-repeating letters:

Find 4 sets of 5-letter words using these non-repeating letters: N, C, A, V, M, S, E, Y, U, R, O, F, G, T, I, L, H, K, P, D
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3 votes
1 answer
198 views

A strange corporate

The employees of corporate "Clocks" have a fixed rule for working hours. All the employees start working at 16:00 and finish their work by 21:00. They take exactly one break during that time....
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3 votes
2 answers
130 views

Productive Neighbours

Seven tiles need to be placed so that one is placed in each of the curved "regions" formed by the three circles. One tile has been placed for you. Each circle has a corresponding statement. ...
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11 votes
1 answer
309 views

The Monopoly tournament's secret prize

The image below is the aftermath of a secret tournament of Monopoly played here on PSE. Akin to something that might come out of a subreddit like r/anarchychess, the board has been massively scrambled ...
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  • 1,219
3 votes
0 answers
131 views

Why do I have so many unanswered puzzles?

I can't understand. I mean, I'm trying to be interesting. Maybe I'm just bad at this. Huh, maybe I should try clickbait... or something special... another type... no, not just another type... GOT IT! ...
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2 votes
0 answers
113 views

What is an EQÜAL WORD (patent pending)

An EQÜAL WORD (patent pending) is a special type of word. You'll know it when you see it. Here are some examples, sponsored by the original, @JLee! What is an EQUAL WORD, and why is it called that? ...
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0 votes
1 answer
99 views

Mice and their relations

In a colony of $(m n+1)$ mice, must at least one of the following statements be true? If so, why? There is a set $A$ of $(m+1)$ mice none of which is a parent of any other in the set. There is an ...
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  • 5,268
3 votes
1 answer
133 views

Find all solutions to a sum of fractions [closed]

Find all the solutions to: $$\frac{1}{x}+\frac{2}{y}-\frac{3}{z}=1$$ where $x, y, z$ are positive integers.
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  • 5,268
3 votes
2 answers
150 views

How high does the ladder reach up the wall?

A ladder of length $l$ rests against a vertical wall. Suppose that there is a rung on the ladder which has the same distance $d$ from both the wall and the (horizontal) ground. Find explicitly, in ...
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  • 5,268
2 votes
1 answer
69 views

What size square grid can you tile?

A tiling of an n × n square grid is formed using 4 × 1 tiles. What are the possible values of n? A tiling has no gaps or overlaps, and no tile goes outside the region being tiled.
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  • 5,268
6 votes
1 answer
699 views

What Am I At 7?

At 1 I was born when my parents parted, And no folds were used. So that's how I started. At 2 I was famous since ages ago, But looked more like three and continued to grow. At 3 I was cover for a ...
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  • 13.1k
4 votes
1 answer
135 views

Show there is always a pair at least 16 apart

The integers 1 to 4 are positioned in a 6 by 6 square grid as shown and cannot be moved. The integers 5 to 36 are now placed in the 32 empty squares. Prove that no matter how this is done, the ...
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  • 5,268
14 votes
2 answers
727 views

Alchemy in a Tin Kit

As usually happens when rummaging through one's grandparents' attic, I unwittingly discovered a seemingly ancient papyrus manuscript. It was stored in an old tin box along with some utensils. I ...
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  • 5,148
8 votes
2 answers
667 views

I've Got You Surrounded!

I'm in your house, workplace, and more. Some say I improve the decor. To measure me, you measure twice, But four times to be more precise. My pet's known for its speed. My best friend's name is Matt. ...
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  • 13.1k
7 votes
0 answers
134 views

A Key Game of Battleship

What two relevant words are encoded in this game? The stuff in the trays doesn't matter too much
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  • 11.8k
-1 votes
0 answers
148 views

випадкові прапори (Євробачення за)

🇮🇸 🇳🇱 🇪🇸 🇳🇱 🇸🇪 🇫🇮 🇺🇦 🇪🇸 [remember chad moves] By the way, I've tried RussiaTunlucky, Thomas Jefferson, a CharlieBrowner, and others. Hint Time! Hint двa!
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3 votes
1 answer
212 views

My strategy shall reveal you my name

Note: Knowledge is about a rather famous element of a rather widespread genre, so maybe not as exclusive as your average knowledge.
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-1 votes
2 answers
134 views

Letters in a Circle [closed]

Bob drew 6 letters into a circle. A, B, C, D, E, F. I don't have a graphic, but imagine those letters into a circle, with A at the top. Bob goes clockwise through the circle, writing every third ...
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  • 109
22 votes
1 answer
2k views

–– –― ―― ‧‧ MORSE CODE –— ―— —— —— –‧ ‧—

—- -– ‧‧ ―― -― ―– ‧‧ –— –‧ ―— –- ‧- ‧— ―- ―– -‧ ‧‧ —‧ –― ―- -― ―― ‧— ‧— –– ‧– –― ‧― -― –– -- ? ―― ‧‧ –— ‧– –― ‧― ‧— ! Inspired by ⠀⠀⠀⠀⠀⠀⠀⠀ ⠀⠀⠀⠀⠀⠀⠀⠀⠀
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  • 4,507
8 votes
3 answers
1k views

Elegant solution to this digit puzzle

Puzzle The letters $a, b, c, d, e$ and $f$ represent single digits and each letter represents a different digit. They satisfy the following equations: $$ a+b=d, \quad b+c=e \quad \text { and } \quad d+...
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  • 5,268
4 votes
1 answer
250 views

Bertrand's Ballot Theorem

A total of X voting papers for candidate A and Y voting papers for candidate B were cast in one section during the election. Where X > Y At the end of election day, the voting papers were counted ...
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  • 43
1 vote
0 answers
91 views

Image steganography: find the song lyrics hidden inside the image

I created this puzzle by myself. And I am absolutely sure I am the first one to come up with the method to convert encoded messages to images. You will be given a ...
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3 votes
0 answers
158 views

Merely Players they

What is the relationship shared by the following celebrities? Deneb Betelgeuse Antares Aldebaran Altair Rigel Adhara (besides the obvious fact that each is an astronomical object comprising a ...
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  • 5,148
-11 votes
1 answer
59 views

Kindly break this code [closed]

axca apax a xadxaght dzaazy, whala a paxdazad, waak axd waazy, avaz xaxy a qaaaxt axd cazaaaz valaxa af fazgattax laza— Whala a xaddad, xaazly xappaxg, zaddaxly thaza caxa a tappaxg, Az af zaxa axa ...
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3 votes
1 answer
159 views

What is a Wyrrd™?

In honor of the long-running What is a Word/Phrase™ series started by JLee with a special brand of Phrase™ and Word™ puzzles, came up with this puzzle myself. There's a special rule that can be ...
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2 votes
1 answer
84 views

Bits and pieces of maps?

Your friend texts you this image. What does it mean? Note: I created this puzzle. Good Luck!
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  • 847
5 votes
2 answers
295 views

Please respond Mark!

I have been trying to contact my son Mark for past 4 days, I hope he is alright. My 17 year old son went to attend "Mathematics Summer Camp", I am really eager to know about the camp, his ...
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13 votes
1 answer
228 views

It's a... Ohh... puzzle (BpFp)

I'm looking for a 5-letter word. ...
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  • 13.9k
4 votes
1 answer
167 views

Rileys From The Grave

My prefix is a veggie, My infix is... though, it's on the interblags [citation: xkcd] My suffix is to eat, in Spanish, in English, in Spanish, And altogether I am not GERMANE, but am GERMAN. My ...
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-6 votes
1 answer
84 views

"type":"excalidraw/clipboard"

Decode it The following encoded message decodes to TEST: ...
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-3 votes
1 answer
283 views

I start with the good and end with the bad

I start with the good and end with the bad I start with the good and end with the (sort-of?) bad My second letters spell poet I rhyme with rest Old Clues:
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