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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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 ...
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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 ...
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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 ...
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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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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 ...
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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, ...
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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 ...
• 5,878
227 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 ...
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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 ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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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 ...
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298 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 ...
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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 ...
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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+...
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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 + ...
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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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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: ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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631 views

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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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660 views

When is my birthday?

Who am I? When is my birthday?
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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 ...
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557 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 ...
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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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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 ...
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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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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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156 views

Copy that solution

This copy machine program prints the solution to a well-known puzzle.  Explanation of the syntax will follow. What solution will be printed for which well-known puzzle?  EXECUTION CODE .--> ...
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A Grand Game (Find two words)

Find 2 relevant (but not strictly related) words using a logical method. One ends in 'R', the other in 'E'. The method should be one which leads to the exact and specific letters for each word (no ...
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208 views

Some blissfully ignorant math?

I was playing around with the code for my game the other day in an effort to create some unique effects. One thing I created was what I called an "ignorant assignment" in which I applied ...
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This Unusual Year

Our current year, 2021, has the unusual property that the digital sum (the sum of the digits) of its square is precisely equal to its digital sum squared. Indeed: 2021^2 = 4,084,441, whose digital sum ...
209 views

Powerful Octagon

Place different integers on the vertices of an octagon so that the sum of the integers in any two vertices joined by one of its edges is a power of 2. Do so in such a way that the largest integer used ...
352 views

The Thieves and the Gold Bars II: Greed and Distrust

Two thieves, Bo and Jo, steal 7 gold bars and are driving away when their car is wrecked in an accident. They-and the loot- is intact. They are at Point A at 8 PM and must go to Point B which is 1 ...
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