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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Oh dang, I have to change my whole answer!
One day, you enter your math classroom. On the board, there are the words POP QUIZ.
Dang it! Was it about fractions? you knew you were bad with fractions.
You look down.
$\begin{array}{|cc|} \...
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Sudoku like you've never seen it before
I've spent this week trying to create a difficult logic puzzle which is a combination of two Sudoku varaints, 'Samuari Sudokus' and 'Pseudokus', and this combo is unlike anything you can find online. ...
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re-re-reCAPTCHA
Last Friday, I was feeling a bit sad because I hadn't earned much rep recently, so I decided to try this awesome sock puppet thing everyone's been raving about. I logged out of my normal Puzzling ...
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A 16 Clue Sudoku Puzzle (but the kings can't be in check)
An entry in the 19th fortnightly challenge...
Above is a 9x9 "chess" board with some pieces already laid out, your goal is to fill the board completely, following standard Sudoku rules (i.e. every ...
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Six pyramids in a cube
This question is from the German mathematics competition Känguru der Mathematik. In this competition students have to solve 30 mathematical tasks like this in 90 minutes without calculator. Actually ...
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Five Slitherlinks
Solve five Slitherlinks, each with a unique solution.
Please say a word regarding (or show an image depicting) each solution method.
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Can you stop the rambling rook?
This is a chess puzzle someone showed me a long time ago. If you already know this puzzle please give the others a chance to solve it first. This puzzle was originally created by Otto Gallischek and ...
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TRUMP to BIDEN : This transition won't be easy
Can you change the word TRUMP to the name BIDEN in 10 steps or less by
changing one letter at a time?
Each change must result in a valid word from MW dictionary.
No proper nouns, abbreviations or ...
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The hardest crossword you'll do today!
This could well be the most difficult crossword you do today!
Please note that the use of Google and other search engines is STRICTLY FORBIDDEN.
(Of course, I have no way of policing this, but if ...
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Unusual letter combinations
This is an entry in the Fortnightly Topic Challenge #41: Short and Sweet.
English spelling is very strange. Sometimes you encounter words with letter combinations that would seem entirely ...
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A cubic colored pyramid
While preparing the next puzzle for publishing, I decided to encrypt the file to protect it, but something went wrong or maybe I entered the wrong command because the puzzle was encrypted, yes, but ...
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Word that is fun. Nine and one
Starts with a name, ends with a name
Starts with a charge, ends with a charge
Starts with an element, ends with an element
Would be fun to guess this one! (May be more than one?)
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Riley Riddles in Reverse
In the all-famous Riley riddles, you have to guess one word from clues about its prefix, infix and suffix. Here, instead,
You get three words.
You must find one solution word that you can attach.....
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Ten girls around a table
Ten girls are sitting around a table.
Each of them picks a real number and whispers it to the two neighbors immediately to the left and to the right. (Hence: each girl communicates one number, and ...
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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.
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First digit of 3^2020
Inspired by
The last digit for 3^(2019)
Can you find the first digit of 32020 without a computer?
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MASTERING Sudoku
Fill the grid with letters M, A, S, T, E, R, I, N and G.
Standard Sudoku rules apply.
Additionally, the words on the right-hand side must appear in the given orientation (across/down). Each word ...
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2 vs. 1.005^200
Without using a calculator or a computer can you determine which of these two numbers is bigger: $2$ or $1.005^{200}$ ?
I saw this puzzle in a YouTube video, which I will post later.
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Three missing digits in 42 factorial
When calculating $42!=42\cdot41\cdot...\cdot2\cdot1$ the result is
$42! = 140500611775287989854x14260624y511569936384z00000000$
However three digits have been replaced by $x$, $y$, and $z$.
Can you ...
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Parallelisation
An entry in Fortnightly Topic Challenge #32: Grid Deduction Hybrids
Puzzlers, I am presenting a set of six duo-grids! Of course, I need to tell you how they work - you are given a grid. Looking at it,...
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How can 3 queens control the white squares?
It is well known that there is no way of arranging 4 queens on a checker board in such a way that every square is occupied or threatened.
Now consider a slight variation where we only need to cover ...
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A triangle formed of three letters
Consider a downward-pointing triangle of letters X, Y, and Z formed by the following algorithm.
Start with a sequence of 10 letters each of which is X, Y, or Z.
Under each row, construct the next row ...
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Breaking the record
There is a record whose value is expressed by a natural number. (The value is strictly discrete, not only continuous and then rounded to a natural number.) However, after the record is once ...
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Sum of the first 86 square roots
Without using a calculator or a computer, can you compute the sum of square roots of the first 86 natural numbers, rounded to the nearest integer? In other words, we are looking for $\sqrt{1} + \sqrt{...
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Computation without a computer
In the number $(1+\sqrt{3})^{2015}$, what is the 224th digit after the decimal point?
You may NOT use a calculator, computer, or any electronic aid to answer this question. Only pen(cil), paper, and ...
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A Secret Job . . . but what is it?
Mr. Peters, a freelance muscle-for-hire sort of fellow, had been manning his desk for days now waiting for something to do when at last the phone rang. A job! The nerdy sounding person on the other ...
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Another Easy Mate in 1
Standard chess rules apply, the board is not rotated (i.e. white pawns move upwards), no lateral thinking is needed. Simply find the one move for white which mates the black king.
This puzzle was ...
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Uh oh, the propeller fell off
I was rummaging through a trunk in the attic when I found this vintage game. It is some sort of pinwheel or propeller mounted on a board. The propeller has a cryptic series of letters painted on it, ...
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PSE Advent Calendar 2021 (Day 20): Candy Cane Sudoku
This puzzle is part of the Puzzling Stack Exchange Advent Calendar 2021. The accepted answer to this question will be awarded a bounty worth 50 reputation.< Previous Door Next Door >
So I was ...
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The No-Straight Maze
Consider the following maze.
You can walk on the black lines, and your aim is to go from the green at the maze's bottom to the red on the left side. However, each time you reach an intersection of ...
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A logician's Bingo
Mark some cells on the following Bingo board, so that all statements in marked cells are true AND all statements in unmarked cells are false.
A Bingo here is a set of five marked cells in a row, ...
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RIDDÅL - another unfinished flat-pack puzzle
This is an entry to the 19th Fortnightly topic challenge
Yesterday I got a package in the mail. Attached to its top was a letter:
Dear Alconja,
That's strange, I thought... Must have gone to the ...
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Superhero words!
Quietly walking among us are words which are actually superheroes in disguise! Just as Diana Prince spins around to become Wonder Woman, some seemingly ordinary words can spin around to reveal their ...
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What is my favorite brand of pen?
This is an entry to the Monthly Topic Challenge #3: Pencil and Paper Games
Given the following valid "tic-tac-toe" boards:
What is my favorite brand of pen?
Other possible tags to check ...
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Some numbers are more equivalent than others
[Second part and bounty challenge appended in May 2020]
ALL ANIMALS ARE EQUAL
BUT ...
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Sudoku in the third dimension (3D Sudoku)
People seemed to enjoy my last Sudoku variant puzzle - Samurai Pseudoku, so I spent this week making another! This one is going to require using logic you've never used before...
The last one was a ...
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Like totally amazing interchangeable sister outfit accessory swapping or whatever
OMG, me and my sister are like total BFFs and we share clothes like all the time! We soooo have the same sense of style and we borrow stuff from each other like every single second!
We don't even ...
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A six letter body part
The question relates to a recent puzzle: One is outstanding, another doesn't belong : Says Grandpa
Take the word PARENT for example.
If you take 2 consecutive letters out, the remaining four ...
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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 ...
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Find 77777 solutions
You have three flat pieces, as shown:
Arrange them flat, without overlap, such that the shape formed by the black parts is congruent to the shape formed by the white parts. Rotation and reflection ...
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Knight tour on a racetrack
Help the chess knight complete four clockwise laps on this racetrack, so that he lands on every square and never lands on the same square twice! The final square the knight lands on will be the same ...
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A wordsearch for today
Sixteen 4-letter words have been concealed in the grid below, as well as one word that is much larger.
Can you find all seventeen words?
Text version of the wordsearch (for copy-paste purposes):
<...
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Someone has vandalised this long division. Can you reconstruct it?
Oh dear, someone has vandalised this long division.
They've replaced every digit either with a wrong digit or a hyphen.
Your task: reconstruct the entire thing. There's no remainder.
Please show all ...
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Escape from Sudoku!
An entry in Fortnightly Topic Challenge #50: Escape Rooms
I hesitated to enter this in the Escape Room FTC, but I definitely was inspired by the challenge to create this puzzle, and it is, in some ...
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Square Spin #1: Sun and Moon
Defining Square Spin
Lets play a game!
The aim of this game is to transform one image into another using the least amount of moves possible. Here is what a move consists of:
...
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Save now! All the digits at half the price
... or double the price depending on where you're coming from
Consider the set $PD10$ of pan-digital ten-digit numbers, i.e. positive whole numbers whose decimal representation has each of the digits ...
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Quartum non datur
Can you give a good rational approximation of
$$\sqrt[3]2 \times \sqrt[4]2$$
without doing any significant maths?
Hint:
Attribution: Mine.
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Which two houses didn't get any mail that week?
Postman delivers the mail in the small village. This village has
exactly ten houses, numbered from 1 to 10.
In a certain week, he did not deliver any mail at two houses in the
village but at ...
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Step into the Octagram
The diagram below shows a partially-filled "octagram". Step into it, if you dare!
At every vertex in a long word.
Flowing into every vertex are two short words. Anagrammed together, these two short ...
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