Most active questions
103 questions from the last 30 days
39
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4
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2k
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The Worst Possible Chess Move
Bad, even very bad chess moves are nothing out of the ordinary. Every single player will have had their fair share of stupid blunders like hanging a queen in an otherwise completely winning position. ...
- 11k
15
votes
5
answers
2k
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On the island everyone worships exactly one god, but how many are liars?
Beginner puzzle (suitable for people who are new to puzzle solving).
The population of the island of Pianosa is 100. Some of the inhabitants always lie; the others always tell the truth. Each islander ...
- 32.1k
14
votes
5
answers
2k
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prisoners riddle - a button, a light and a timer
Here is (yet another) prisoner riddle. I made it up (maybe it was asked before, but to the best of my knowledge I'm the first to ask it - correct me if I'm wrong).
There are 1000 prisoners who are ...
- 143
14
votes
4
answers
1k
views
Numbers which are the product of two numbers that share no digits
Say a positive integer is cute if it can be written as the product of two other integers greater than 1 that share none of their digits.
a) Find 12 consecutive integers all of which are cute.
b) Are ...
14
votes
3
answers
1k
views
1 vs. 3 hide and seek challenge
There are four people playing hide and seek in a 1 vs. 3 format. Three of them are hiders, and the fourth is the seeker trying to find the hiders.
The game starts by the hiders choosing which zones to ...
- 865
12
votes
6
answers
1k
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Crossing a square pond with beams
Here is a classical mathematical puzzle:
In the middle of a square pond lies a square island (whose sides are aligned with the sides of the pond). On the island is a tower with a princess locked ...
- 121
8
votes
6
answers
838
views
Sum of a sequence
The last two days I have dreamt of solving a puzzle to escape hospital, and I just woke up so wanted to jot this down quick.
Imagine a snake with some number of segments. The segments' labels are $(1,\...
- 219
19
votes
3
answers
1k
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Two semicircles in a parallelogram
Two congruent semicircles (blue) are inscribed in the two triangles formed by the short diagonal (black) of a parallelogram (also black) as shown below. The short diagonal has the same length as the ...
- 20.4k
17
votes
3
answers
2k
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Complete the integer sequence: 10, 11, 12, 13, 14, 20, ?, ?, ?, ?
Here is a sequence I happened to work out, although I am certainly not the first one.
Can you fill in the missing numbers?
10, 11, 12, 13, 14, 20, ?, ?, ?, ?
NB: The sequence ends after the last ...
- 181
15
votes
3
answers
1k
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What's my favorite snack?
Author's note: This puzzle was originally written for the 2025 Stanford Puzzle Haunt.
The author does not actually enjoy the snack of this puzzle.
Across
6. Bay Area telecom giant founded by two ...
- 1,954
19
votes
3
answers
934
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Undecidable Checkmate
While playing chess, I had a momentary dizzy spell which erased most of my short-term memory. I knew only the current position, and that I was playing White, and that all play so far had been legal, ...
- 2,585
14
votes
2
answers
1k
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Vertical bars...or I mean...well, you'll get what I mean
Find the hidden answer which describes what you've found.
...
- 53.8k
14
votes
3
answers
895
views
A "crappy" pentagon puzzle
Lately, we've had plenty of puzzles based on the regular pentagon and its geometric properties. So I propose one that literally brings it all together.
Use eleven copies of the larger (left) piece ...
- 2,714
8
votes
4
answers
1k
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Find the missing digits in 1/2024
1/2024 is equal to $0.000\overline{a9407114b245059c88d375}$.
Can you find the values of a, b, c, and d without using a calculator?
Long division is trivial. Can you use other ways to find the missing ...
- 1,935
13
votes
2
answers
906
views
Three-cushion billiards challenge.
World champion three-cushion billiards player can perfectly make a billiard ball end where asked for (if possible), on a standard rectangular shaped competition table.
The champion now, for ...
- 3,026