Questions tagged [no-computers]
A puzzle designed to be solved without using calculators, online decoders, or computer programming. Using a computer to type and post the answer is allowed; the spirit of this tag is to make people solve the puzzle on their own.
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Regarding the universe; life, death, neutrons, stars; everything
My brother Yzarc recently returned from his summer road trip, so I went to visit him.
He seemed unusually quiet, sitting pensive in a chair and watching the clouds. This was unusual, since typically ...
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Computer Puzzle - Arithmetic Of The Day
Harou, a Japanese teacher in the school, noticed a ship made of paper outside her office.
When she unfolds the paper, she saw something strange.
There is something that looks like a riddle, followed ...
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3
votes
2
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Cube the digits and carry on
Take a number between 2001 and 2100 inclusive. Cube the digits of the number and add them together, then repeat the process with the new sum and restart the process over and over. For example if I ...
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Solve the magic square
My friend gave me the following magic square to solve
$$\begin{bmatrix}\frac23&5&?\\\frac19&?&?\\?&?&?\end{bmatrix}$$
I can solve it. Can you?
You must provide logical ...
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9
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1
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Whose birthday is it?
A group of people have gathered for a birthday celebration. Their ages are related as follows:
The product of the 1st person's and the 2nd person's ages is $311\frac{2}{3}$ plus the 3rd person's age.
...
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2
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I'll give you the instructions, you give me the answer
- perform handshake
- install es on both ends
- pause process in exce
- swap chang.exe
- combine previous and modify
- terminate communication
Hint 1
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3
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A Kind of Unique Prime Number
A Prime number with the following properties
Less than 7 digits and more than 3 digits
ALL digits in the number are Prime numbers-- some repeated.
All individual digits in the number add up to a ...
- 39.2k
17
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2
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What to make of $\!\:\tt puzzle.\!txt$?
Puzzling Stack Exchange:
Don’t even ask where I found
the old printout, below, of an uncommented computer program.
As I am a leading-edge software solutionaut
hone-tuned for elegantly annotated ...
- 21.8k
15
votes
1
answer
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Words with Alchemists
You are probably familiar with Word Ladders, where you attempt to transform one word into another by switching one letter at a time, with each transformation forming a new word. This puzzle is similar....
- 26.5k
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2
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Letters to Numbers: What goes in the blank circle?
This is a letter to number conversion and pattern puzzle.
What number goes in the blank circle and why?
Each letter is a distinctly seperate digit from 0 to 9. ( There are 10 letters representating ...
- 39.2k
7
votes
0
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Hand tiling - 4x inflated pentominoes with pentominoes and tetrominos
This is a manual tiling puzzle. Difficulty level always hard to estimate, but I would say a few minutes per solution for an accomplished solver, all the way to just about impossible for someone like ...
- 3,798
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too easy puzzle? Try it first!
Arrange the numbers $1$ to $9$ to replace letters $A$ to $I$ so:
$(A+B+C+D)-(E+F+G+H) = I$
Too easy? Too many answers? Try it first!
Then explain why.
- 17.8k
4
votes
2
answers
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Can you find the key move?
I've created this chess problem for today. it's White to move and their pawns move upward. Can you find the key move? Have fun, and no computers are allowed!
Checkmate In 5 Moves
Addendum 11/6/2021: ...
- 8,253
7
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3
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Perfect power nim
Let $m,n$ be positive integers. Ann and Ben has $m$ stones, and each of them takes exactly the perfect power of $n$ stones ($n^k$, where $k$ is a nonnegative integer) in order, starting from Ann. Who ...
- 5,560
8
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4
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The broken wheel
In a regular polygon, we can connect six of the vertices to form a convex hexagon.
I construct a hexagon by picking six vertices out of a regular $n$-sided polygon. In this hexagon, if you connect the ...
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3
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Fill in numbers on the cube ... again!
You are given a cube. You are told to fill in each face randomly with some of the numbers $4, 5, 6, ..., 11$, with no repetition. What is the probability that for each two faces that are connected by ...
- 26.8k
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Today is a sad day
Today is a sad day - Today, it was supposed to be my big day to shine! But unfortunately that is no longer the case.
I have heard from others here that puzzle-making is a great way to drown out one's ...
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4
votes
1
answer
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Fill in numbers on the cube!
You are given a cube. You are told to fill in each vertex with the numbers $4,5,6,...,11$, with no repetition. What is the probability that for each two vertices that are connected by a common edge, ...
- 5,560
3
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2
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335
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10
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4
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The Eighth Color
For this puzzle I've made, guess what is the missing color. You can't use a computer to find the solution. But once you know you have it, you are allowed to use a computer, mostly to select a RGB ...
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2
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Escape from your friend!
I saw this interesting problem in a Mathematics book in Chinese(I translated it):
You and your friend is playing a game. There is a square swimming pool, and you are in the middle of it. Your friend ...
- 5,560
9
votes
1
answer
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Mini 8 queens puzzle
On a 5x5 chessboard, place 5 black queens and 3 whites queens so that no queens are attacking those who are of different color. Furthermore, the numbers indicate how many queens are attacking the ...
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4k reputation special: "I hate square numbers!"
There is a large prison, with exactly 4000 prisoners. The warden noticed that there were too many prisoners, so they lined up all the prisoners, and repeated the following procedure until less than ...
- 5,560
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Square made up with polyominoes
A 3 x 6 rectangle has 2 holes in it as shown. Can you cut it into 3 polyominoes with different areas so that they can form a square? The pieces can’t be flipped when they form the square and two ...
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14
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Pythagorean triplets wheat field
A rectangular field has width $a$ and length $a+1$. We cut it into 3 triangles that all have integer side lengths. If all triangles have a different area, then what’s the minimum value of $a$? Please ...
- 1,943
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votes
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Can you fill $3 \times 3$ magic square?
In the magic square
Each number in the matrix is unique and natural.
Each row, column and the two diagonals add up to the same number (the magic constant).
Can you fill in the missing numbers?
\...
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14
votes
1
answer
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The numbers on blackboard
The numbers $2020,2019,2018,...,1$ are written on the blackboard from left to right.
John repeats the following process until there is only one number left:
John chooses the first two numbers from ...
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3
votes
1
answer
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Find the unique passcode
"Is this the Coldport Lost Property Office? I think I left my puzzle-book on the train this morning, and I was hoping someone had handed it in." The speaker was a tall gentleman with a six-...
user40528
3
votes
2
answers
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A Puzzle about "Codeforces Subsequences"
I'm quite intrigued by an "easy" problem in recent Codeforces contest: Codeforces Subsequences.
In this problem, you have to create a string $T$ as shortest as possible such that $S = $ &...
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A Puzzling Cryptex
I was hanging out in the Puzzing.SE lounge (the beanbag chairs are heaven) when some random person walked up. They said, "I love this place! Would you try my puzzle?" Their puzzle was a cryptex (...
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votes
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Fibonacci progression
In a number sequence, 1, 13, 169 and 2014 are respectively the first four terms of the sequence. The next terms are equal to the sum of the four numbers that precede them. For example, the fifth term ...
- 1,943
13
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Maximise your gold!
You met a genie. He gets $150$ magic lamps out, which are numbered from $1$ to $150$. You have to colour each lamp red or blue. After colouring, the genie will count the number of triples $T$ of magic ...
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3
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Lottery strategy
In a city, the official lottery consists of scratch cards that cost 10 bucks each. Each scratch card contains 36 squares with a hidden number on each square : 21 of them are “zeroes”, 9 of them are “...
- 1,943
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In honour to 2004
222444 is the smallest number that is divisible by 2004 and only contains the digits 2 and 4. What’s the next number that has the same properties?
Hint:The number is 11 digits long.
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4
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Numbers that are the sum of the cubes of their digits
There are just four 3-digit numbers which are the sums of the cubes of their digits. For example:
$370 = 3^3 + 7^3 + 0^3$ and $371 = 3^3 + 7^3 + 1^3$.
Without using a calculator/computer, can you ...
- 33.2k
3
votes
1
answer
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Multiples of their reversals
8712 and 9801 are the only 4-digit numbers which are multiples of their reversals:
8712 = 4*2178 and 9801 = 9*1089.
Without using a calculator/computer, can you find two 5-digit numbers with this ...
- 33.2k
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votes
2
answers
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A Covid-19 puzzle: Alcohol for your School!
You are the principal of a primary school in HK. Schools are resuming soon, and you have to ensure that your school have enough alcohol. Each of the 30 classrooms should have a bottle containing 500mL ...
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5
votes
2
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Multiplicative sudoku (don’t use computers please)
If I place all the numbers from 1 to 9 in a 3x3 grid and I add the products of each row and column, then what is the minimal and the maximal sum?
For example, the sum is 450 on the picture above
- 51
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1
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Functional Equation: Squeeze it
Determine whether there exists a function $f:\mathbb{R}\rightarrow\mathbb{R}$ such that $$f\big(x^3+x\big)\le x\le\big(f(x)\big)^3+f(x)$$ for all $x\in\mathbb{R}$.
Source: Math Excalibur Volume 22 No....
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2
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Find a factor #1
The series of Find a factor puzzle is started by Culver Kwan, and asks the solver to identify a factor of a certain large number within a certain range using some mathematical identities. This should ...
- 5,560
8
votes
2
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A risky investment
I invested $1000 into shares. On the first day the share price went up by 10%. On the second day it went down by 10%. This process continued - the share price would go up by 10% on odd days and down ...
- 33.2k
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Another follow the path of relation through the grid
Inspired by Galen's series of puzzles...there is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-...
- 26.5k
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Gaby's Puzzle (Primes Around a Circle)
To keep them busy during lockdown, Gaby asked her children to find a way to place the first sixteen primes (2 to 53) around a circle so that either the sum or difference (or both) of any two of them ...
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Logical task for math
I have one Math puzzle to which I think I found the solution but wanted to check your opinion on it. The puzzle is the following:
George has 1 banknote of 100 (the currency does not matter. Lets name ...
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1
answer
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Follow the path of relation through the grid #9
There is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-right corner of the grid. Each square can ...
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3
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1
answer
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Follow the path of relation through the grid #8
There is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-right corner of the grid. Each square can ...
- 2,296
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7
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What number is that ? Asks Grandpa
"So here is a number between 1 and 60" Says Grandpa
"If you take its WORD anagram and subtract this number you will get
Anagram of the number - number > 5
What is that number"?
"So it is the ...
- 39.2k
4
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2
answers
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Minimum number of flips required to turn a sequence into alternating A and Bs
You are given this sequence composed of the characters A and B:
A B B B A B B A A B A A B A A B A B A A A B B A B B B A
At ...
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1
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Follow the path of relation through the grid #7
There is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-right corner of the grid. Each square can ...
- 2,296
7
votes
2
answers
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Q-Puzzle on $\mathbb F_7$
My high school math student had to solve this puzzle for his homework. I made it harder by not telling you what is the definition of $\mathbb{F}_7$. Neither why letter Q is used and which of his ...
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