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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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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16 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 + ...
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21 votes
1 answer
518 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): <...
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12 votes
1 answer
527 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: ...
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9 votes
2 answers
483 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 ...
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3 votes
2 answers
183 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 ...
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6 votes
2 answers
441 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 ...
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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 ...
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6 votes
2 answers
551 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 ...
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5 votes
2 answers
520 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 ...
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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 ...
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6 votes
1 answer
756 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, ...
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10 votes
2 answers
506 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 ...
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5 votes
2 answers
218 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 ...
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4 votes
1 answer
650 views

When is my birthday?

Who am I? When is my birthday?
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5 votes
1 answer
182 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 ...
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  • 38.8k
2 votes
1 answer
282 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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28 votes
1 answer
670 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 ...
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3 votes
1 answer
399 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 ...
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13 votes
2 answers
617 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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32 votes
2 answers
3k views

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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  • 11.5k
4 votes
1 answer
127 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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7 votes
3 answers
558 views

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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  • 11.8k
3 votes
1 answer
183 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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4 votes
1 answer
180 views

Fractions and Fractional Numbers

Using fractions and fractional numbers of the digits $1$ to $10$ and only the mathematical operations of addition, subtraction, multiplication, and division, including parenthesis (e.g. $1 + 2 - (3 * ...
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2 votes
2 answers
213 views

Consecutive integers which have digital sums that are not relatively prime

What are ten smallest natural numbers n, such that n and n+1 have digital sums which are not relatively prime?
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2 votes
1 answer
223 views

What number comes next in this evenly doubled sequence?

I've been playing around with sequences lately and found a pretty evenly doubled sequence of single digit numbers: 1, 12, 30, 64, 65, 156, 175, 368, 369, 371, 752, 753, 1524, 1525, 3060, 3073, 6168, ...
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1 vote
1 answer
156 views

An oddly formed sequence?

I've been playing around with sequences lately and came across one that was rather, odd. $101$, $123$, $147$, $189$, $191$, $213$, $217$, $279$, $...$ Hints Let $N_i = 101$... Can you determine the ...
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3 votes
1 answer
462 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 ...
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9 votes
4 answers
1k views

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 ...
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2 votes
2 answers
187 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 ...
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5 votes
3 answers
316 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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11 votes
1 answer
223 views

Tiling three pears with three-pair hexominos

The 21 hexominos below are all those that can be made by joining three dominos together (i.e. they have a perfect matching with respect to the graph of their squares) and are not rectangles. The ...
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6 votes
1 answer
154 views

White to play and mate in 3 - adapted from real game

This is adapted from a real game between GMs where white played the King's Gambit. I changed the position slightly (moved one piece) because there were actually two mates available, with one more ...
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  • 22.3k
-8 votes
1 answer
133 views

Puzzling rectangles [closed]

Can you find two unequal rectangles whose areas add to $5\sqrt5$? No computer solutions please.
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9 votes
3 answers
770 views

Heteropalindromes in a Word Square

Say hello to a not-so-simple, 4x4 word square: This little monstrosity has two rules; to define the first rule, have you ever heard of a heteropalindrome? Strings of letters that form words when ...
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0 votes
1 answer
160 views

How do I ring my friend's doorbell?

My friend, a curmudgeon who dislikes visitors, recently installed a puzzle-doorbell. It consists of ten push buttons in a row, labelled from left to right: ...
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19 votes
3 answers
2k views

The Thieves and the Gold Bars

Two thieves (Rod and Lia) carry out a big heist and steal 16 gold bars. They get away in their car when they run into a bad accident and the car is completely wrecked. Luckily they survive with their ...
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  • 38.8k
3 votes
2 answers
765 views

Most points on a circle

What is the most number of integer lattice points that lie on the circumference of a single circle whose radius is 80 or less? Please no computer computations.
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8 votes
1 answer
1k views

Life, uh, Finds a Way

[Rated PG-13 for language} I saw someone wearing a "Life happens" t-shirt, which is a fine enough sentiment, but not the most common turn of phrase. It made me wonder... How fast can you ...
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  • 3,546
31 votes
2 answers
3k views

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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22 votes
3 answers
1k views

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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  • 31.3k
3 votes
2 answers
242 views

Seven 2s with seven math operations

Linked to A four digit number using exact same 4 digits A number with same repeated digits is called a Repdigit or Monodigit number https://en.wikipedia.org/wiki/Repdigit Can you write an equation for ...
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  • 38.8k
4 votes
1 answer
359 views

Hero Worms and The Minotaur

And so, Wormeus had a great time, eating every apple in sight, surviving several close calls with the Pink Lady Stickotaurs, respawning after the occasional horribly squishy death, exploring different ...
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  • 6,549
8 votes
1 answer
188 views

Going off on multiple tangents

Given two disjoint circles of diameters D1 and D2 draw all shared tangents. Find the intersection points of all pairs of tangents. Discard those collinear with the two circle centre points. Of the ...
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  • 11.6k
7 votes
2 answers
514 views

Triangles to diamonds

Given a triangle ABC with sides a=|BC|,b=|CA|,c=|AB| a diamond is circumscribed around the triangle's incircle. The diamond and the triangle share the corner C along with (part of) sides a and b. ...
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  • 2,816
1 vote
1 answer
124 views

Can you pick up an extra shift?

I was going through some old documents the other day and found some instructions for a one way cipher: Given a word w, iterate over its characters. For each character c, determine if its zero based ...
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12 votes
6 answers
4k views

A four digit number using exact same 4 digits

ABCD is a 4 digit number where A,B,C and D are 4 distinctly separate digits between 1 and 9. Using any of the following math operations and the digits A,B,C and D exactly once get the number ABCD. ...
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  • 38.8k
5 votes
1 answer
124 views

Wormeus and the Multiple Stickotaurs (Part 2)

This is the sixth puzzle in the Wormeus series and the second puzzle involving multiple Stickotaurs and wormhole puns. Wormhole-pairs are indicated with light green lines (note that this was ...
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  • 6,549
8 votes
2 answers
616 views

When was Ensquare born?

Professor Matlogic posed this question to his smartest math student: "Famous mathematician Ensquare was born on this day, this month and this year AD at this time (hour and minutes) pm. True to ...
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