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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47 votes
4 answers
3k views

Five Slitherlinks

Solve five Slitherlinks, each with a unique solution. Please say a word regarding (or show an image depicting) each solution method.
26 votes
2 answers
2k views

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, ...
16 votes
0 answers
1k views

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 ...
4 votes
3 answers
344 views

Laziest Checkmate

Consider a game of chess where White delivers checkmate in their $X^{th}$ move. For all the pieces that remain on the board at the end of the game, consider their Manhattan Distances from their ...
4 votes
1 answer
149 views

Packing the Primes

Here is a 5x4 rectangular wordsearch (area 20) containing the primes between 1 and 100, {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} (numbers in any ...
12 votes
4 answers
643 views

How do I create a sliding-blocks puzzle (specifically like the "Rush Hour" ones) which requires an "ah-hah!" moment?

Background My grandma gave me a set of Rush Hour puzzles as a small child, ever since I could be trusted to not eat the pieces. I still enjoy playing these today and would like to try my hand at ...
10 votes
3 answers
2k views

The Universe's Secret

To find the universe's secret, first solve the Sudoku variant with #s 1-7 only. No number may be repeated on any diagonal. No numbers go in the squares with red or green dots. Then use the solution ...
13 votes
15 answers
8k views

The computer can't do anything I couldn't do with pen and paper

If you want to know how much $3^{100}$ is, you can just type it into a computer and it will spit out a really big number. But that is no fun. The task is to estimate $3^{100}$ with some computation ...
5 votes
6 answers
394 views

How many digits does $7^{100}$ have?

I'd like to estimate $7^{100}$ without using these new-fangled computers everyone is talking about, but I think I need your help. Please estimate $7^{100}$ without the use of a computer. My friend ...
10 votes
2 answers
1k views

A square number that is a concatenation of at least 25 squares

A pen and paper challenge: Write down a number whose square (repetition allowed) is the concatenation of at least 25 nonzero squares. examples 7, 13, 12: Their squares are the concatenation of 2 ...
3 votes
2 answers
218 views

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 ...
1 vote
1 answer
151 views

Determine the hidden digits in this long division puzzle

The following problem was given in the Eureka journal (October 1963/University of Cambridge). This problem can be solved by hand without computers. There is a unique solution. Have fun solving! Fill ...
5 votes
2 answers
349 views

a six-by-six KenKen

The rules of KenKen are as follows: You must fill in the numbers 1 through 6, one number per box, in the grid, so each row and each column contains each number exactly once. Each heavily outlined ...
4 votes
2 answers
312 views

Dark time in prison

You wake up. It is pitch dark. You don't know where you are. You feel groggy. The last thing you remember is being in a bar, a sexy young woman appeared out of nowhere, walked straight at you, ...
6 votes
2 answers
1k views

What are the hidden digits in this long division puzzle?

The following problem was given in the Eureka journal (April 1978/University of Cambridge). This problem can be solved by hand without computers. There is a unique solution. The phrase, "exact ...
3 votes
1 answer
159 views

Sequence of numbers - what comes next? [duplicate]

What is the next number in this sequence, and why? 4 2 3 4 6 2 4 8 3 _? Also, since people here find sequence questions to be arbitrary, the following uses the same rule. What number is next? 4 5 6 4 ...
6 votes
1 answer
428 views

Find all integers n such that $\sqrt{n-4 \sqrt{n-19}}$ is also an integer

The following puzzle is from the December 2012 issue of the Eureka journal (published by The Cambridge University Mathematical Society). Find all integers n such that $\sqrt{n-4 \sqrt{n-19}}$ is also ...
3 votes
1 answer
133 views

Tetromino tilings of a 4x5 rectangle with minimal diversity

This is a relatively easy manual tiling puzzle. In fact the tiling is all done for you, you just have to specify how many of each of the 26 given tilings to use. The puzzle is: Using N complete sets ...
13 votes
1 answer
2k views

The Lufthansa Lottery

In order to pass free time while striking for better pay, some Lufthansa workers organise a lottery where each ticket picks three distinct numbers from $1$ to $11$ inclusive the draw picks five ...
17 votes
7 answers
1k views

Efficient Mowing at PSE

Your task: Find the most efficient mowing path around the dark green bushes that mows (passes over) all of the grass (light green). For those who cannot view the image above, there are 9 rows of 16, ...
53 votes
3 answers
3k views

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 ...
4 votes
1 answer
135 views

Find the 3 Item Amounts

Last week the store's receipt printer removed lines randomly from each item amount. A technician repaired the printer, but now it adds lines randomly to each item amount! The cashier told me that for ...
3 votes
2 answers
715 views

Pan Digital Lucky Seven wants you to figure out all the digits

Given: A, B, C, D, P, Q, R, S, T are distinct digits varying from 1 to 9. AB, CD, PQ, RST are all concatenated Numbers. From the given expression , figure out all the digits to make lucky seven. $$\...
6 votes
1 answer
293 views

Riley-Clued Crossword

The no-computers tag is there only to prevent database dictionary searches. Other computer uses are fine. Below is an ascii version of the image above, for those who cannot view images. All words are ...
5 votes
2 answers
614 views

A Complicated Exercise In Addition

Another day, another walk down to the cafe. I was waiting in line for my coffee, wondering what the barista could do this time to make my name look whack. But as I waddled in line, a curious site ...
18 votes
3 answers
740 views

Find the Two Item Amounts

I bought 2 items yesterday and the receipt was incorrect, so I asked the cashier about it. She told me that The receipt printer had been acting funny recently. The total is always correct, but some ...
3 votes
1 answer
317 views

Will forcing chains break this sudoku puzzle?

I am trying to pick up advanced sudoku techniques by practicing with “difficult” puzzles as suggested by my sudoku app. In this puzzle, I am stuck in the position as shown below. I think I can make ...
0 votes
1 answer
245 views

Sum of digits of numbers

Let S be a function such that S(N) is the sum of digits of N. N belongs to natural numbers, and N < 10²³. N does not contain a zero digit in it. The numbers are in base 10. Find the number of N ...
8 votes
3 answers
1k views

Elegant solution to this digit puzzle

Puzzle The letters $a, b, c, d, e$ and $f$ represent single digits and each letter represents a different digit. They satisfy the following equations: $$ a+b=d, \quad b+c=e \quad \text { and } \quad d+...
12 votes
1 answer
543 views

A massive synonym

Please explain how to assemble the puzzle. Yes, one is missing, but you can follow the >. No computers. Hint: Hint 2: Hint 3: Text version: ...
10 votes
2 answers
590 views

An overconfident grandmaster

Suppose you are playing a grandmaster with the White pieces and you are on the verge of losing the game. The overconfident grandmaster offers you a bet: You will make two consecutive moves with White ...
17 votes
3 answers
2k views

No Computer Allowed (Beware the Eater)

The answer is a relevant single word. No computer or digital calculator allowed. Beware the eater of red herring, if you happen to spot it. 6 - 5 + 4 + 7 = ? 7 + 8 + 8 - (7-5) - (7-1) = ? 6 - 5 + 7 + ...
21 votes
1 answer
572 views

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): <...
3 votes
2 answers
205 views

Using Prime numbers to get 100 and 1000

Using the digits 1 to 9 exactly once create a set of one or two digit prime numbers. Use those prime numbers and the math operations + - / * and parantheses to get 100. Then use those exact same ...
7 votes
2 answers
457 views

It is all in the past

Presented here are questions related to past tense words I researched and googled that resulted in this designed and developed puzzle. Got it? Which past tense word (PTW) is also a past tense word ...
3 votes
1 answer
473 views

A number like waldo?

What is the smallest whole number that when its individual digits are summed, produces a number 4 digits long? For example, the number $5357$ is no where close since $5 + 3 + 5 + 7 = 20$. Note: I'm ...
12 votes
3 answers
1k views

Adding consonants to create an antonym

This is an emotional word with 2 vowels Starting with it create two words by adding 2 different consonants. The two new words are antonyms of each other. See below. What is that word? No programming ...
10 votes
4 answers
531 views

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 ...
6 votes
2 answers
568 views

Five words, Five vowels, Five last names

These five words are from the Collins English Dictionary. Are also last names, And have one vowel difference in exact same location and same consonants in exact same locations. Example : Last Lest ...
10 votes
2 answers
538 views

Permutations of first 10 natural numbers such that all the prefix sums are distinct

I posted this question on Math SE as well. Did not receive any help. This is a question that I was asked in a Quant Interview. I would like you all to have a crack at this. I could not find a problem ...
7 votes
1 answer
1k views

Can you stop the falling piano with 23 nets?

MIT's Baker House has a tradition of dropping an irrepairable piano six floors every Drop Day, the last day one can drop a class without penalty (the 2022 date is 19 April). This year, in order to ...
6 votes
1 answer
850 views

Binary Sudoku Puzzle

The rules of Binary Sudoku are quite simple. It is very similar to regular Sudoku, except here we try to fill a 9x9 board with only black and white tiles following the below rules: Every row, column, ...
5 votes
2 answers
234 views

How many coins did Raj get?

I found a bunch of coins: Quarters (25 cents), Dimes(10 cents) and Nickels(5 cents). The combined amount was a whole two digit number of dollars: that is, no fractional amount. I divided the coins ...
4 votes
1 answer
656 views

When is my birthday?

Who am I? When is my birthday?
5 votes
1 answer
193 views

Fill in the blanks with numbers

A simpler version of this puzzle was by @Sid on PSE Fill in the blanks with the number in words Here is a bit challenging version Fill in the blanks with numbers (in words) for the following: This ...
2 votes
1 answer
365 views

Thirteen Diagonals of a Nonagon

A regular nonagon has 27 diagonals, and these diagonals intersect in the interior of the nonagon at 126 distinct points. Show that it is possible to select 13 diagonals of a regular nonagon such that ...
28 votes
1 answer
738 views

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 ...
3 votes
1 answer
418 views

Genies' chess on a 10×10 board

The work of Hearth Taxel revealed some other results related to genies' chess. For example, there is an arrangement $A$ of pawns on a 10×10 board such that no 3×3 submatrix is empty and $A$ is ...
4 votes
1 answer
431 views

Around The World

It's White to move and win against Black. Black plays optimally. Have fun! Oleg Pervakov and Karen Sumbatian, Shakmaty v SSSR 1990 P.S.-To me, it’s crazy that the title hasn’t been taken yet! Hint:
14 votes
2 answers
788 views

PSE Advent Calendar 2021 (Day 4): Decorating with Ingrid Deduction

This puzzle is part of the Puzzling StackExchange Advent Calendar 2021. The accepted answer to this question will be awarded a bounty worth 50 reputation. < Previous Door Next Door > "...

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