Questions tagged [no-computers]

A puzzle designed to be solved without using calculators, online decoders or computer programming. You're still allowed to use a computer to post the solution; Stack Exchange doesn't support smoke signals yet.

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7
votes
3answers
213 views

Perfect power nim

Let $m,n$ be positive integers. Ann and Ben has $m$ stones, and each of them takes exactly the perfect power of $n$ stones ($n^k$, where $k$ is a nonnegative integer) in order, starting from Ann. Who ...
3
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1answer
131 views

Fill in numbers on the cube … again!

You are given a cube. You are told to fill in each face randomly with some of the numbers $4, 5, 6, ..., 11$, with no repetition. What is the probability that for each two faces that are connected by ...
19
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1answer
3k views

Today is a sad day

Today is a sad day - Today, it was supposed to be my big day to shine! But unfortunately that is no longer the case. I have heard from others here that puzzle-making is a great way to drown out one's ...
6
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2answers
331 views

Tempoverlustspiel

Tempoverlustspiel-A German word that roughly translates to "loss of tempo game." An interesting chess term that I leaned a while ago. With White to move in the below position, how many moves ...
4
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1answer
164 views

Fill in numbers on the cube!

You are given a cube. You are told to fill in each vertex with the numbers $4,5,6,...,11$, with no repetition. What is the probability that for each two vertices that are connected by a common edge, ...
5
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3answers
862 views

4k reputation special: “I hate square numbers!”

There is a large prison, with exactly 4000 prisoners. The warden noticed that there were too many prisoners, so they lined up all the prisoners, and repeated the following procedure until less than ...
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2answers
268 views

Elementary word-search

Here's a simple wordsearch: ...and the text version: ...
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2answers
1k views

Escape from your friend!

I saw this interesting problem in a Mathematics book in Chinese(I translated it): You and your friend is playing a game. There is a square swimming pool, and you are in the middle of it. Your friend ...
9
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1answer
363 views

Mini 8 queens puzzle

On a 5x5 chessboard, place 5 black queens and 3 whites queens so that no queens are attacking those who are of different color. Furthermore, the numbers indicate how many queens are attacking the ...
9
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2answers
251 views

Square made up with polyominoes

A 3 x 6 rectangle has 2 holes in it as shown. Can you cut it into 3 polyominoes with different areas so that they can form a square? The pieces can’t be flipped when they form the square and two ...
12
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1answer
517 views

A Puzzling Cryptex

I was hanging out in the Puzzing.SE lounge (the beanbag chairs are heaven) when some random person walked up. They said, "I love this place! Would you try my puzzle?" Their puzzle was a cryptex (...
4
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1answer
172 views

Can you fill $3 \times 3$ magic square?

In the magic square Each number in the matrix is unique and natural. Each row, column and the two diagonals add up to the same number (the magic constant). Can you fill in the missing numbers? \...
14
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1answer
624 views

The numbers on blackboard

The numbers $2020,2019,2018,...,1$ are written on the blackboard from left to right. John repeats the following process until there is only one number left: John chooses the first two numbers from ...
3
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1answer
106 views

Find the unique passcode

"Is this the Coldport Lost Property Office? I think I left my puzzle-book on the train this morning, and I was hoping someone had handed it in." The speaker was a tall gentleman with a six-...
3
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2answers
441 views

A Puzzle about “Codeforces Subsequences”

I'm quite intrigued by an "easy" problem in recent Codeforces contest: Codeforces Subsequences. In this problem, you have to create a string $T$ as shortest as possible such that $S = $ &...
3
votes
2answers
272 views

Fibonacci progression

In a number sequence, 1, 13, 169 and 2014 are respectively the first four terms of the sequence. The next terms are equal to the sum of the four numbers that precede them. For example, the fifth term ...
12
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5answers
2k views

Maximise your gold!

You met a genie. He gets $150$ magic lamps out, which are numbered from $1$ to $150$. You have to colour each lamp red or blue. After colouring, the genie will count the number of triples $T$ of magic ...
10
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3answers
3k views

Lottery strategy

In a city, the official lottery consists of scratch cards that cost 10 bucks each. Each scratch card contains 36 squares with a hidden number on each square : 21 of them are “zeroes”, 9 of them are “...
8
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3answers
594 views

In honour to 2004

222444 is the smallest number that is divisible by 2004 and only contains the digits 2 and 4. What’s the next number that has the same properties? Hint:The number is 11 digits long.
6
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4answers
760 views

Numbers that are the sum of the cubes of their digits

There are just four 3-digit numbers which are the sums of the cubes of their digits. For example: $370 = 3^3 + 7^3 + 0^3$ and $371 = 3^3 + 7^3 + 1^3$. Without using a calculator/computer, can you ...
3
votes
1answer
76 views

Multiples of their reversals

8712 and 9801 are the only 4-digit numbers which are multiples of their reversals: 8712 = 4*2178 and 9801 = 9*1089. Without using a calculator/computer, can you find two 5-digit numbers with this ...
9
votes
1answer
283 views

Simple Homeworlds puzzle

On this site, we have numerous chess puzzles. however, we do not seem to have any Homeworlds puzzles, the game of space kings (yes this can be tagged outer space thank you very much.) Hence, here is ...
6
votes
2answers
453 views

Logical task for math

I have one Math puzzle to which I think I found the solution but wanted to check your opinion on it. The puzzle is the following: George has 1 banknote of 100 (the currency does not matter. Lets name ...
7
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2answers
684 views

A Covid-19 puzzle: Alcohol for your School!

You are the principal of a primary school in HK. Schools are resuming soon, and you have to ensure that your school have enough alcohol. Each of the 30 classrooms should have a bottle containing 500mL ...
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2answers
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 ...
5
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1answer
503 views

Some luck involved

Can you guess the theme? OK, feel free to reverse image search, it's been many days now. Slight Tip: Tip 1: Tip 2: Last Tip:
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2answers
576 views

Multiplicative sudoku (don’t use computers please)

If I place all the numbers from 1 to 9 in a 3x3 grid and I add the products of each row and column, then what is the minimal and the maximal sum? For example, the sum is 450 on the picture above
9
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1answer
298 views

Functional Equation: Squeeze it

Determine whether there exists a function $f:\mathbb{R}\rightarrow\mathbb{R}$ such that $$f\big(x^3+x\big)\le x\le\big(f(x)\big)^3+f(x)$$ for all $x\in\mathbb{R}$. Source: Math Excalibur Volume 22 No....
10
votes
2answers
275 views

Add a divisor! A game

Let $k$ be a positive integer. Amy and Ben are playing a game, with the number $1$ written on the whiteboard initially. Amy and Ben do the following in order, starting with Amy: Suppose the number on ...
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2answers
125 views

Find a factor #1

The series of Find a factor puzzle is started by Culver Kwan, and asks the solver to identify a factor of a certain large number within a certain range using some mathematical identities. This should ...
25
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6answers
1k views

Some numbers are more equivalent than others

[Second part and bounty challenge appended in May 2020]           ALL ANIMALS ARE EQUAL    BUT ...
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2answers
637 views

A risky investment

I invested $1000 into shares. On the first day the share price went up by 10%. On the second day it went down by 10%. This process continued - the share price would go up by 10% on odd days and down ...
8
votes
2answers
277 views

Another follow the path of relation through the grid

Inspired by Galen's series of puzzles...there is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-...
11
votes
1answer
304 views

Gaby´s Puzzle (Primes Around a Circle)

To keep them busy during lockdown, Gaby asked her children to find a way to place the first sixteen primes (2 to 53) around a circle so that either the sum or difference (or both) of any two of them ...
4
votes
1answer
84 views

Follow the path of relation through the grid #9

There is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-right corner of the grid. Each square can ...
7
votes
1answer
180 views

Follow the path of relation through the grid #2

There is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-right corner of the grid. Each square can ...
6
votes
1answer
158 views

Follow the path of relation through the grid #3

There is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-right corner of the grid. Each square can ...
5
votes
2answers
169 views

Follow the path of relation through the grid #5

There is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-right corner of the grid. Each square can ...
5
votes
1answer
87 views

Follow the path of relation through the grid #6

There is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-right corner of the grid. Each square can ...
4
votes
1answer
142 views

Follow the path of relation through the grid #7

There is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-right corner of the grid. Each square can ...
3
votes
1answer
94 views

Follow the path of relation through the grid #8

There is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-right corner of the grid. Each square can ...
22
votes
7answers
4k views

What number is that ? Asks Grandpa

"So here is a number between 1 and 60" Says Grandpa "If you take its WORD anagram and subtract this number you will get Anagram of the number - number > 5 What is that number"? "So it is the ...
10
votes
5answers
1k views

Knight on the keyboard

You are given a QWERTY keyboard, and are allowed to choose where you wish to start. You are only able type in the same way a knight is able to move on a chessboard (but in this case, on the keyboard). ...
6
votes
2answers
195 views

Q-Puzzle on $\mathbb F_7$

My high school math student had to solve this puzzle for his homework. I made it harder by not telling you what is the definition of $\mathbb{F}_7$. Neither why letter Q is used and which of his ...
4
votes
2answers
187 views

Minimum number of flips required to turn a sequence into alternating A and Bs

You are given this sequence composed of the characters A and B: A B B B A B B A A B A A B A A B A B A A A B B A B B B A At ...
3
votes
1answer
98 views

Follow the path of relation through the grid #4

There is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-right corner of the grid. Each square can ...
13
votes
1answer
268 views

Follow the path of relation through the grid #1

There is a relation between rectilinear-adjacent squares such that there is a unique rectilinear path from the top-left corner of the grid down to the bottom-right corner of the grid. Each square can ...
7
votes
3answers
189 views

The ceiling function and powers of 2

How many integers $1\le x\le2048$ such that $$\Big\lceil \frac x{2^n}\Big\rceil$$ is not a multiple of five for all nonnegative integers $n$? This problem is a 2020 contest problem which has finished....
9
votes
1answer
477 views

Find The Common Pattern In These Words

You are a super spy, typing on your QWERTY keyboard, when suddenly you received an urgent call from your boss, Caesar. He had urgently called you, defying all protocols, as he wanted to inform you ...
6
votes
1answer
146 views

Darwin Fooling Dalton

Dalton wants to measure the effectiveness of a treatment for a particular type of plant and, being a good scientist, decides to have a control group that does not have the treatment. He is able to ...

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