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1500 questions
25
votes
3 answers
Twenty-four trees in eighteen rows of four
A very old puzzle, #146 from American Agriculturist, April 1865:
How may twenty-four trees be planted in exactly eighteen rows, with four trees in each row? A row consists of a number of trees in a straight line. The same tree can be part of…
Will Octagon Gibson
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25
votes
12 answers
Kill the jokers! - Part 1
The famous and ruthless explorer Wyoming Wilbert reports in one of his books that he once visited an island inhabited by jokers and truth tellers. Truth tellers always tell the truth, whereas jokers sometimes lie and sometimes tell the truth.…
Haobin
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25
votes
1 answer
I end up as a Criminal
I am (kind of) a number
That ends with a number
I get enraged
When you add a starting number
I become a criminal
When you add a different starting number
What four letter word am I?
DrD
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25
votes
12 answers
Can the cop catch the thief?
The cop and the thief, both mathematical points, live in an open interval $(0,1)\subset \mathbb{R}$. That is, their universe is a line segment of length 1 without the 2 endpoints. We know that both move simultaneously and continuously at a maximum…
Eric
- 6,488
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25
votes
3 answers
Rock climbing at the Tokyo Olympics
The idea for this puzzle came from my friend Jan. The puzzle is based on real world events from the Tokyo Olympics.
The Olympic rock climbing preliminary round has 20 climbers. Each climber competes in 3 separate events, where they rank from 1st to…
Dmitry Kamenetsky
- 35,897
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25
votes
5 answers
retsubkcolB Spelled Backwards
How would you enter
retsubkcolB
spelled backwards into the comment box below and press the "Add comment" button (nothing will happen, as there's only 11 letters) using at most 10 clicks in total?
You should end up with something like…
risky mysteries
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25
votes
1 answer
Sudoku in Technicolor!
An entry in Fortnightly Topic Challenge #47: "Wacky Sudokus"
This puzzle consists of three overlapping Sudokus, coloured red, blue and green, so each cell will contain three digits, one of each colour. Taken individually, the digits of each colour…
Jeremy Dover
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25
votes
1 answer
The Blank Sudoku
An entry in Fortnightly Topic Challenge #47: "Wacky Sudokus"
(h/t to Beastly Gerbil, whose 1,2,3... Trinary!!! puzzle provided inspiration for this puzzle)
This puzzle is a normal Sudoku, with each digit from 1-9 appearing once per row and column,…
Jeremy Dover
- 27,440
- 3
- 66
- 157
25
votes
1 answer
Chain Puzzle: Tabletop Games #10 – Risky Finale
This is the tenth and final Chain Puzzle in the Tabletop Games series, in which all puzzles are themed around board games, card games, tile games, and the like. Once this puzzle is solved, this Chain Puzzle series is complete!
The answer to the…
Jafe
- 78,615
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25
votes
1 answer
Suspected felicide in the Schrödinger household
Police officers entered the home of Dr. Erwin Schrödinger. The neighbours had reported that the doctor had locked his cat in a box and was subjecting it to "particle physics", whatever horrors that may mean. As there were lives at stake – nine,…
Jafe
- 78,615
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25
votes
4 answers
Hacked maps, back in the UK
[TL;DR? - scroll down to to Summary section for the key points]
[Inspired by Jeremy Dover's "Google (Maps) Hacking" puzzle. That and my previous puzzle on a similar subject may give "spoilers" for this one, or they may distract...]
I returned from…
Steve
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24
votes
21 answers
When you take away two
I am an odd number.
When you take away two,
I become even.
What am I?
Edit: @hexomino got my original answer but I have come up with another valid answer.
Edit 2: @QuantumTwinkie got my other answer. It's really cool to see so many other…
DenverCoder1
- 10,472
- 20
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24
votes
2 answers
What if I told you that guessing in Sudoku is very bad and might give you a bad karma?
Yesterday, I tried to solve a regular Sudoku puzzle. Of course, the Sudoku puzzle had a unique solution. But, I was feeling a little lazy, so, rather than solve the puzzle properly, I made guesses! At every step, I put a random number in one of the…
athin
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24
votes
1 answer
Can you name the Country Code™?
Given the country codes of 10 countries in the chart below, can you figure out the country code of Brazil?
Country
Country…
DenverCoder1
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- 89
24
votes
3 answers
Is there any easy way to solve this lock puzzle?
https://js13kgames.com/games/lock-puzzle/index.html
The link provides an online puzzle game of $16$ tiles in the form of a $4 \times 4$ matrix of which some entries are in the form of vertical tiles and other in the form of horizontal tiles…
math maniac.
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