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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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5 votes
1 answer
421 views

Oh no, my chocolate banana puzzles are not unique!

There is a hidden message (7, 2) inside the solutions of the nine puzzles. An answer will only be accepted if it correctly identifies said message. Here are the Chocolate Banana puzzle rules. Each ...
18 votes
4 answers
3k views

Prime to Prime: Get all first 25 Prime Numbers using up to 4 Primes

The first 25 Prime Numbers are 2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97 Using up to 4 prime numbers and the following mathematical operations, get all the 25 primes. + ...
13 votes
4 answers
2k views

Can you color the 8x8 grid red and blue?

Consider an 8x8 grid made up of 64 unit squares. The goal is to color the 64 squares red or blue so that the following two constraints are satisfied: ROWS: For every pair of adjacent rows, exactly ...
3 votes
1 answer
167 views

Long Division when it is almost, but not entirely, wrong

Hmm, my last long division puzzle (Reconstruct a long division given less than a quarter of the digits, and all of those are wrong) didn't last the night. So let's try to make it harder. All of the ...
9 votes
1 answer
212 views

Reconstruct a long division given less than a quarter of the digits, and all of those are wrong

Inspired by "The Puffin Book of Brainteasers" I decided to try my hand at creating a long division missing digits problem where all of the displayed digits are wrong. On searching I found ...
8 votes
3 answers
3k views

Split a number in half, sum it, square it and get the number back

The number 3025 when split in the middle gives us 30 and 25. 30+25= 55. The square of 55 is 3025. What other 4 digits numbers have this property i.e. when the 4 digit number is split in the middle, ...
19 votes
3 answers
1k views

Keys and Locks Puzzle

Let $a,b,n$ be positive integers in which $a,b\le n$. You are locked in a room, with $n$ distinguishable keys and $n$ distinguishable locks in it. You know that each lock can be unlocked by a unique ...
5 votes
1 answer
172 views

Current record for minimally clued 7x7 Hidato (16 clues)

Background Back in March, I posted this question on the Puzzling Stack Exchange asking how many clues were needed to create a 4x4 Hidato puzzle with a unique solution. Sometime after this, I took a ...
16 votes
2 answers
2k views

What's the missing pattern? 3x3 grid, dot pattern

What is the missing piece to this pattern? Got it as a quiz at work - no one here knows what it is!
6 votes
2 answers
533 views

Create an empty 8x8 One Up puzzle with a unique solution

Rodolfo Kurchan created a wonderful new grid puzzle called One Up that you can play on his website. There is one main rule: Each horizontal and vertical sequence of N cells between walls, must contain ...
11 votes
1 answer
458 views

Best Wishes for 2024: Four empty Suguru (Tectonic) puzzles

To continue last year's tradition, hereby four empty suguru puzzles. Rules of suguru: Each square gets a number so that each block of n squares has the numbers 1..n, and neighbouring squares (...
3 votes
1 answer
153 views

Themed 7x21 Chocona

Chocona rules differ from Chocolate Banana rules. There is a hidden message inside the solution of the puzzle. An answer will only be accepted if it correctly identifies said message. The message is ...
5 votes
1 answer
195 views

Themed 13x9 Chocolate Banana

There is a hidden message inside the solution of the puzzle. An answer will only be accepted if it correctly identifies said message. P.S. I promise this is my last Chocolate Banana puzzle of the ...
11 votes
2 answers
513 views

Prime and Composite 6x6 Chocolate Banana

The number of chocolates (black regions) is prime. Normal Chocolate Banana rules apply. Rules: Paint some of the cells black. Black cells linked orthogonally must always form a rectangle (or a ...
7 votes
1 answer
266 views

11x13 Chocolate Banana Followup

Your goal is to maximize the absolute difference of the numbers marked ?. (? marks indicate region areas. They may or may not ...
9 votes
1 answer
245 views

9x13 Chocolate Banana Puzzle $\pi=\frac{43}{3.7^2}$

Since 37 is my favorite integer and π is my favorite number, here's another puzzle: Normal Chocolate Banana rules apply. Rules: Paint some of the cells black. Black cells linked orthogonally must ...
14 votes
1 answer
1k views

10x10 Choco Banana

Normal Chocolate Banana rules apply. Rules Paint some of the cells black. Black cells linked orthogonally must always form a rectangle (or a square). Non-blacked cells linked orthogonally must not ...
10 votes
2 answers
375 views

The game of 42: 10 cards to make 42

This is a game inspired by other recent questions. It is a 2-player game. The game is played with 10 cards numbered 1 to 10 and 2 positions or stacks. The game starts with all cards in stack 1. The ...
3 votes
1 answer
237 views

Minimally clued 4x5 Hidato (4 clues)

Puzzle attribution: Me :) Background So as you might or might not know, I have been studying the minimum number of clues needed to force a unique solution in Hidato for variously sized boards. I ...
2 votes
1 answer
353 views

Find the ciphering method 4

Link to the entire series. The message: ...
7 votes
1 answer
201 views

4×6 Rectangle With A Twist

It is known that a $4\times6$ grid can be colored with two colors such that no four cells of the same color form an axis-aligned rectangle. The only valid coloring, up to permutation of its columns, ...
19 votes
2 answers
1k views

Which expression is larger?

Without using a calculator/computer, please show steps to determine which expression is larger: $(2^{90})!\quad vs.\quad2^{30!}$
6 votes
2 answers
800 views

Interesting equation with fractions

Find distinct positive integers $a$, $b$, $c$ and $d$ such that $$\frac{1}{a}+\frac{1}{b}+\frac{1}{c}-\frac{1}{d} = \frac{1}{a} \cdot \frac{1}{b} \cdot \frac{1}{c} \cdot\left( -\frac{1}{d}\right)$$ No ...
3 votes
1 answer
364 views

Place numbers 1 through 9 in boxes (☐☐×☐=☐☐+☐☐=☐☐)

So recently I was scrolling through Youtube when I came across this video from MindYourDecisions that was about solving a legendary math puzzle. The puzzle: Place the numbers 1 through 9 in the ...
23 votes
1 answer
875 views

Invalid Jigsaw Sudoku Layout

The Jigsaw Sudoku Layout below is invalid (no Latin Squares exist for it). Why? Please find a short, yet complete, explanation (no computations involved). ...
19 votes
1 answer
954 views

Anyone Seen My Snorkel?

This is part 54 of the puzzle series Around the World in Many Days. Each part is solvable on its own. mqoı ugw7qж , zqv qw o h6ım v6ınɔ ugwo7 | zo 78վn £þxm εıqm conxnøqxw v8կox h6ımw , დnɔ þn 7დvn ...
10 votes
1 answer
553 views

Multiplying to reverse digits

Today I noticed that $294$ is a multiple of $49$, which is the last two digits of $294$ reversed. How many other numbers have this property? That is, how many three-digit numbers have a factor which ...
10 votes
1 answer
465 views

What Language Is This?

It is the year 2204, and we have finally found intelligent extraterrestrial life. We are delighted about this, so we asked the aliens, ...
6 votes
0 answers
260 views

Mate-in-25 tsumeshogi

This is apparently the first shogi-related question on this site! Yay! Anyway, this is a mate-in-25 tsumeshogi. Sente (the player with the pieces pointing up) is to move and by an uninterrupted series ...
6 votes
2 answers
436 views

Pawns and a chessboard with no three aligned

This little problem crossed my mind and appeared to be not quite trivial. How can you place P pawns on a chessboard with the constraint that no pawn is exactly midway between two other pawns? Sure ...
9 votes
1 answer
601 views

Hardcore Lighting - Excalidraw

Each yellow cell is a light that shines in exactly one direction, horizontally, vertically, or diagonally, endlessly, and goes through any block as long as the block is not a wall. Black cells do not ...
-6 votes
1 answer
153 views

Why does the grid look different?

Relatively easy puzzle: Why does the grid look different?
4 votes
1 answer
513 views

Surely it's not Sny again

Each dot is a light, which shines in exactly one direction, horizontally, vertically, or diagonally (like a bishop, in a 45-degree angle). Lights shine through each other. Uncover the secret message ...
3 votes
1 answer
272 views

7 Lights in 7 Tetrominos

In each orange tetromino, place a light that shines in all directions horizontally and vertically. Light shines through tetrominoes. Tetromino tiles are considered unlit initially and may be lit. ...
6 votes
2 answers
200 views

River crossing cats and dogs

A farmer and his $n$ cats and $m$ dogs are on one side of a river. There is a boat that can carry the farmer and at most $k$ animals at once. The boat doesn't move without a person operating it. The ...
6 votes
5 answers
3k views

Math is Awesome

I have a shirt. It says that $AWE+SOME=MATH.$ A, W, E, S, O, T, M, and H are not necessarily distinct positive integers from $0$ to $9$. The goal is to find the maximum possible value of $MATH.$ If ...
12 votes
1 answer
823 views

27 spaces, 27 curious places

Grid 1: Grid 2: Grid 3: Find the meaning behind these images. Hint 1: Hint 2: Hint 3:
3 votes
0 answers
90 views

Another hand tiling puzzle - 8 convex shapes from 7 polyiamonds

Arrange the 7 polyiamonds in the image into 8 different convex shapes. One after the other, not simultaneously... Rotating and flipping allowed. No gaps or overlaps. Should be a fairly easy puzzle.
37 votes
13 answers
9k views

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 ...
3 votes
0 answers
133 views

Hand tiling polyiamond puzzle. Non-trivial

Group these 30 polyiamonds into five sets of six, then use each set of six to make five different convex shapes. There are some repeated polyiamonds, no set of six may contain a duplicate. The convex ...
3 votes
1 answer
265 views

Constructing 2024 from the first 7 natural numbers

Can you use each number 1, 2, 3, 4, 5, 6, 7 exactly once, the four operations +, -, *, / and the parentheses to construct the number 2024? Bonus: can you find multiple distinct solutions? No computers ...
11 votes
2 answers
1k views

Important Alien Message

A strange alien transcript, alongside what is believed to be a partial key, was recovered the other day. Scientists aren't sure what the message might contain, but theories point to some sort of ...
-2 votes
1 answer
245 views

First five digits of a googol factorial

Based off of: MacPOW 1134 Without using a calculator/computer, can you determine the first five digits of $10^{100}!$ (a googol factorial)? I came up with this when trying to solve the question this ...
5 votes
2 answers
438 views

SAD!!!...System Access Denied..you got three minutes to input three digit passcode

Hexagon is a super secret system with varying levels of access. Users do not have to remember any password. They just have to answer the questions posed by Hexagon strictly in the allotted time. Today ...
8 votes
2 answers
749 views

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 separate digit from 0 to 9. (There are 10 letters representing 10 ...
2 votes
0 answers
122 views

Make three different convex shapes with four polyiamonds, by hand. Five times

To while away the endless holidays. Start with the four polyiamonds in row one. Arrange them without gaps or overlaps (flipping/rotating allowed) in a convex shape. Repeat for two more convex shapes, ...
6 votes
1 answer
450 views

Where are your kids?

You are a mom (or dad) with two boys, Stephen and Philip, aged 8 and 10. While you have been out in the garage, they have been in their separate rooms doing their homework before being allowed to play....
10 votes
2 answers
643 views

It ended with an AFTERSHOCK

I started with a single-letter English language word. At each step, I added a letter of my choice, then re-arranged the letters to make a new word. I ended up with: AFTERSHOCK How did I get there? ...
6 votes
1 answer
354 views

Add as few plus signs as possible to make equation true

To allow new users to solve this puzzle and earn reputation points, I encourage all users whose reputation is 200 or more to not post an answer until 48 hours after this question is posted. Thank you! ...
18 votes
2 answers
781 views

PSE Advent Calendar 2023 (Day 9): The Peppermint Twist

This puzzle is part of the Puzzling Stack Exchange Advent Calendar 2023. The accepted answer to this question will be awarded a bounty worth 50 reputation.< Previous Door Next Door > This puzzle ...