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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7
votes
1answer
498 views

A special number

Here is a nice puzzle from my friend. Can you find a number that is a product of two consecutive primes and when multiplied by its own reversal produces a palindrome? The answer may surprise you. No ...
5
votes
3answers
282 views

A Circle of numbers

Just saw a Circle of numbers on my Whats App message (source not listed) which is as following Arrange numbers 1 to 32 in a circle such that any two adjacent (neighboring) numbers add up to a perfect ...
8
votes
2answers
367 views

Rack 'Em Up! 🎱

In a game of English eight-ball pool, a set of 15 balls are arranged or 'racked' in the shape of an equilateral triangle. In order for the balls to be racked fairly, they must be arranged like so: <...
35
votes
3answers
6k views

First digit of 3^2020

Inspired by The last digit for 3^(2019) Can you find the first digit of 32020 without a computer?
4
votes
1answer
144 views

Find the fastest stalemate for Black!

In the below position, how many moves will it take for Black to be stalemated? Black moves first, and both sides are working together. Black's pawns are moving down. Have fun solving! Zdravko Maslar, ...
6
votes
1answer
205 views

Down The Board-Selfmate In 10 Moves

Here's a miniature selfmate puzzle that I composed today. I just got an idea and I managed to successfully create it. I got the basic idea down to just 9 pieces, none of which are promoted. It's White ...
6
votes
1answer
264 views

An Artistic Bunch

Luke, Clive, Anton and Paul are four talented creative artists, one a dancer, one a painter, one a singer, and one a writer. (Though not necessarily respectively.) Luke and Anton were in the audience ...
7
votes
2answers
1k views

I have a bad feeling about this country name

What is the longest country name that can be fully anagramed into one word from the Merriam-Webster dictionary? Please use this site for the list of countries. Minimum length 8 letters. If a country ...
17
votes
9answers
4k views

Solitaire Chess

A friend of mine got me Solitaire Chess for Christmas years ago. I set up the board below. Is it possible to solve it? If so, what is the solution? (No programs allowed- Use only your brain.) Rules: ...
7
votes
2answers
339 views

Pentomino tiling on wrap-around 5x5 grids

It is known that P pentominoes cannot tile a 5x5 square board. Q1: If the east and west edges of the 5x5 square board are "wrapping around" (if you move a piece through one of the edges, the ...
2
votes
4answers
457 views

Crossing out every second number

Write down all integers from 1 to 1000. Cross out the first number and every second number after that. So you will cross out 1, 3, 5 and so on. Now repeat the process exactly - cross out the first ...
3
votes
1answer
208 views

n rows and 18 columns

I haven't posted for a long long time, so here is an interesting combinatorics problem! There is a table with 𝑛 rows and 18 columns. Each of its cells contains a 0 or a 1. The table satisfies the ...
7
votes
1answer
247 views

Stochastic Taxicab Path

A city's roadworks is laid out as a perfectly rectangular tiling. A commuter within this city has to travel to work a distance of 17 blocks east and 7 blocks north each day, and tries to take the same ...
12
votes
2answers
399 views

A fraction puzzle

This is a puzzle with both the computer-puzzle tag and the no-computers tag. We have the following list of five fractions: $$11/5, 30/77, 1/11, 21/2, 5/7.$$ Starting with an integer $x$, we perform ...
2
votes
1answer
111 views

Does this alphametic have only one solution?

I could only get one answer for the following alphametic. Can you confirm? ETAS / (E * T * A * S) = SEAT - SATE All 4 lettes are separate digits from 1 to 9. ETAS, SEAT and SATE are 4 digit numbers ...
3
votes
2answers
243 views

Yet another mixed sum

An instance of this puzzle is here: https://www.theguardian.com/science/2020/nov/16/can-you-solve-it-the-srcmalbed-nmebur-plzuze a) It has been swhon taht to raed a txet the oedrr in wihch the ...
13
votes
1answer
545 views

The tip of a colorful triangle

Original source: Problem 1 of British Informatics Olympiad 2017, Round 1 You're given a bunch of red (R), green (G), and blue (B) balls. I arrange some balls on a line. Then I ask you to complete the ...
13
votes
3answers
2k views

Want to go from MANILA to UGANDA

How do you get from the word MANILA to UGANDA in the shortest time? You can change up to 3 letters at a time to form a new 6 letter word which MUST be either a country name or a capital of a country. ...
10
votes
10answers
4k views

A Body Part inside another Body Part

In one of his silly question moods, Grandpa says: "Can you name a body part that is entirely inside (within) another body part but some distance away?" Taking the clue from his last question ...
7
votes
7answers
305 views

Chess Construction Challenge #3-The Inverse Babson

Another day, another task! Today's challenge is to construct four positions, with White to move and win, such that: In each position, White's move is to promote to a particular piece, for a position ...
18
votes
1answer
834 views

Honeybee Hangover

A drunken honeybee lands on a completely random hexagon of a large triangular section (depicted below) of its hive, and then every second afterwards, takes a step to a completely random adjacent ...
5
votes
1answer
176 views

Particular Diophantine equation [closed]

There are four natural numbers $a$, $b$, $c$ and $d$ such that $a<b<c<d$. They satisfy the following equation: $a^2$+$b^2$+$c^2$+$d^2$= $abcd$ What is the smallest possible value of $d$? This ...
5
votes
2answers
182 views

7x7 Knight's tour: Minimal proof for universality on black squares

We already know that 7x7 board cannot have a closed Knight's tour, and it cannot start or end at a white square if R1C1 is black. But our knowledge about 7x7 Knight's tour is still limited. So here is ...
3
votes
1answer
360 views

Solve the Lyne puzzle

This puzzle comes from the game Lyne. The rules: Start and end at the shape with a white dot in the middle Only connect same colours together Lines cannot cross each other All points must be ...
12
votes
2answers
439 views

The art of computer programming

EDIT: I know we are not supposed to edit in new requirements after first posting but as far as I understand it this requirement is implicit in all questions here: Explain your answer! At least a ...
0
votes
1answer
118 views

The largest lettered word which you can make and continue make words from it by deleting $1$ letter from it everytime [duplicate]

Ok, here is a simple puzzle to think :- Find the largest lettered word such that deleting one letter at a time can give you a meaningful word in each step . Note that only deletions are allowed, in ...
43
votes
5answers
9k views

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 ...
6
votes
4answers
499 views

Backwards pawns

Part One: Reach the above position from the starting position Part Two: Find the fastest way to get to this position. Answering part one will get you an upvote, answering part two gets the checkmark!
6
votes
1answer
113 views

Sudokus everywhere 2

Every 9x9 box is a valid sudoku, making 4 sudokus in all. Hopefully this one is a little more challenging than the previous one. I tried keeping the clues symmetric, but didn't quite manage. Enjoy!
60
votes
2answers
4k views

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. ...
18
votes
1answer
784 views

Sudokus everywhere!

Every 9x9 box is a valid sudoku, making 9 sudokus in all. I'm not sure how hard it is as I started solving it with just a few clues, then added more whenever I got stuck. Enjoy!
9
votes
2answers
175 views

4x4 grid equations version 2

I decided to make another one of these, because they are fun and this one is rather different. Can you place all numbers from 1 to 16 into cells, such that the following 8 equations hold? Note that ...
4
votes
2answers
868 views

Move 2 or 3 spaces in this 5 by 5 grid

You have a 5 by 5 Board as shown. You start from the S (Center) position. You can: 1 Move TWO or THREE spaces only 2 You can move Vertically or Horizontally or Diagonally but only in a straight ...
10
votes
1answer
570 views

4x4 grid equations

Can you place all numbers from 1 to 16 into cells, such that the following 8 equations hold? Note that the operator "/" only works for non-remainder division, i.e. you can have "8 / 4&...
12
votes
1answer
498 views

An odd looking Sudoku

Somewhat in the spirit of Stiv's This new puzzle type needs a name, can you solve this odd looking Sudoku and give it a name?
13
votes
4answers
2k views

77-digit number divisible by 7 with seven 7s

The smallest number divisible by 7 with seven 7s is trivially 7777777. Then, what is the greatest 77-digit number divisible by 7 which contains seven 7s?
4
votes
0answers
184 views

What is the shortest English–language sentence which contains 25 unique letters? [closed]

There is a lot of literature on the subject of short English pangrams, that is, sentences that contain every letter. But I am curious what the shortest, or at least some of the shortest, sentences are ...
6
votes
3answers
551 views

How to divide their loot? The thieves' dilemma

Three thieves rob a jewelry store at gunpoint and end up with the following loot. 10 necklaces 8 bangles 6 rings It so happened that the jewelry was antique and valuable. They asked the scared ...
3
votes
1answer
223 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
2answers
234 views

Coffee theorem puzzle [duplicate]

I am back yet with another puzzle, my last one was made this morning, and this one is a copied one from an app/website called Brilliant. So, this is especially for those who do not have Brilliant ...
7
votes
4answers
1k views

Change Four to Nine in fewest steps

Change the word FOUR to the word NINE by changing only one letter at a time. The change must result in a 4 letter word from the MW dictionary and cannot be an abbreviation,acronym, anagram or a ...
20
votes
2answers
1k views

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 ...
7
votes
1answer
230 views

Balancing a yardstick

There is a known trick to this, so “no computers” may be used to look up the answer. Alice gives Bob a wooden yardstick with a small weight secured to one end and says, “See if you can find the ...
9
votes
1answer
295 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 ...
7
votes
2answers
365 views

Unlock the safe!

There is a (very insecure) safe, which has three digits in the lock. Each digit can only be $0,1,2$. The user choose a password made up with three $0,1,2$ digits, and the safe can be unlocked if at ...
11
votes
1answer
278 views

Regarding the universe; life, death, neutrons, stars; everything

My brother Yzarc recently returned from his summer road trip, so I went to visit him. He seemed unusually quiet, sitting pensive in a chair and watching the clouds. This was unusual, since typically ...
9
votes
1answer
382 views

The Lucky Number

Lucky numbers are 4 digit numbers that have the following property: they are equal to the sum of the fourth power of their digits. Therefore, they can be expressed as follows: $$1000a+100b+10c+d = a^4+...
4
votes
2answers
157 views

Computer Puzzle - Arithmetic Of The Day

Harou, a Japanese teacher in the school, noticed a ship made of paper outside her office. When she unfolds the paper, she saw something strange. There is something that looks like a riddle, followed ...
8
votes
1answer
389 views

Whose birthday is it?

A group of people have gathered for a birthday celebration. Their ages are related as follows: The product of the 1st person's and the 2nd person's ages is $311\frac{2}{3}$ plus the 3rd person's age. ...
3
votes
2answers
139 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 ...

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