Questions tagged [puzzle]
Recreational mathematics or puzzles with serious mathematical content. Note that math contest problems are generally considered off-topic.
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References and upper bounds for the SONNAT tiling game?
Introduction
In a video released about a month ago, Pembesita describes1 a tiling game called SONNAT: Same Orientation Neighbour Not Allowed, Tiling.
In the single-player game2, the player may employ ...
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A puzzle with magic Egyptian tilings
Background
I've recently been devising a puzzle that incorporates elements from Egyptian fractions, magic squares, and tilings. The objective of the puzzle is to tessellate a square with sides of ...
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Does a function from $\mathbb R^2$ to $\mathbb R$ which sums to 0 on the corners of any unit square have to vanish everywhere?
Does a function from $\mathbb{R}^2$ to $\mathbb{R}$ which sums to 0 on the corners of any unit square have to vanish everywhere?
I think the answer is yes but I am not sure how to prove it.
If we ...
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Proof that a pandiagonal Latin square of order $n$ exists iff $n$ is not a multiple of $2$ or $3$?
A pandiagonal Latin square of order $n$ is an assignment of the numbers $\{0,\ldots,n-1\}$ to the cells of an $n \times n$ grid such that no row, column, or diagonal of any length contains the same ...
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Dissecting using a ruler and compass
The problem is to cut a regular hexagon into parts that can be put together (without overlaps or wasting any parts) to make an equilateral triangle using only a ruler and compass (and scissors).
What ...
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Optimal search puzzle
Consider the following puzzle: On the integer line from 1 to $t$ (top, let's say 1000 for this example), you have two operators: uniform random on 1 to $t$, and subtract 1. What is the optimal ...
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100 mathematicians each have a numbers written on their foreheads
100 mathematicians each have a number written on their foreheads, visible to all but themself. One day, a meta-mathematician comes by and remarks, "I see all the numbers are distinct natural ...
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Making perpetual motion machine from candy-sharing cats
It is well known that cats can be turned into perpetual motion machines under the right circumstances. Candy-sharing cats are such wonderful creatures that come in infinite supplies, labeled 1,2,3,...
...
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How many convex polygons can be made from $n$ identical right angle triangles?
Whilst working on a Tangram problem, I came across the need to find the total number of convex shapes that can be produced from $16$ identical (isosceles) right angle triangles (since the Tangram can ...
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Big triples in a matrix
Consider an $n\times n$ real matrix $A=(a_{ij})$ with non negative entries. Assume that
- the sum of the three largest entries in each row is a constant $R$ (the same for all rows),
- the sum of the ...
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A New York Times tiles-based graph theory question
The New York Times has a daily puzzle named Tiles that works as follows. Start with $m$ squares (in the official version, this is 30, in a 6x5 grid), and a set of $p>4$ possible patterns (typically ...
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Undecidable puzzles
There are plenty of popular NP-hard puzzles,
for example, generalized Sudoku ($n^2 \times n^2$-board), Flow (I cannot give a source for this), Minesweeper, etc.
Recently, I read a bit about aperiodic ...
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Integers in a triangle, and differences
I read about the following puzzle thirty-five years ago or so, and I still do not know the answer.
One gives an integer $n\ge1$ and asks to place the integers $1,2,\ldots,N=\frac{n(n+1)}{2}$ in a ...
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God's number for the $n \times n \times n$-cube
This is a question about Rubik's Cube and generalizations of this puzzle, such as Rubik's Revenge, Professor's cube or in general the $n \times n \times n$ cube.
Let $g(n)$ be the smallest number $m$, ...
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R. Smullyan's "Lady or the tiger", Ch. 5, Island of Questioners, problems 11-12 [closed]
I cannot understand the context and formulation of these problems.
The inhabitants ask only questions answerable by yes or
no. Each inhabitant is one of two types, A and B. Those of
type A ask only ...
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Has there been any new development on the Freudenthal Problem?
Background
I have seen a few variants of this Sum-and-Product puzzle in the past. The premise of these puzzles is as follows
Sam hears the sum of two numbers, Polly the product. The numbers are ...
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100 Prisoners, 100 Boxes: Proof of Optimality
There's a chestnut about 100 prisoners, labeled 1 through 100, and 100 boxes, each with a number 1 through 100 in it. Each prisoner, completely independently of the others, tries to find the box which ...
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God's number for higher dimensional Rubik's cubes
In this MO question, user Martin Brandenburg asks about God's number for $n \times n \times n$-cubes for $n>3$. Here, God's number $g(n)$ was defined as the smallest number $m$ such that every ...
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Game on groups (generalization of spinning switches puzzle)
Alice and Bob are playing a game as follows:
Initially
There're two subgroups $A,B$ of Sym(n) known to both Alice and Bob
There're $n$ slots $S_1, \cdots, S_n$ and $n$ boxes $B_1, \cdots, B_n$. ...
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Can an infinite number of mathematicians guess the number in a box with only one error?
In this question the following observation was made:
Consider a sequence of boxes numbered 0, 1, ... each containing one real number. The real number cannot be seen unless the box is opened.
Define ...
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Mathematical model for Hanoi Towers
The strategy for the Hanoi Tower puzzle is quite simple. It is based on parity only. In an $n$-pieces puzzle, $2^n-1$ moves are sufficient to carry the whole pile from one pole to another one. My ...
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The mower's challenge
Weeds have taken over the paths (two squares). If mowed, they don't grow back, but unmowed weeds spread at speed $1$ along the road. What's the minimum speed of the mower to get rid of all the weeds? ...
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What is a good formalization of this classic math puzzle? [closed]
Here is a classic math olympiad problem (but this is NOT my question!): Each of the girls A and B tells the teacher a positive integer but neither of them knows the other's number. The teacher writes ...
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probability and math puzzle books/references [closed]
Hi All,
I'd like to solve some math puzzles, especially in the context of probability theory, but I'm open to other areas too. The kind of problems that does not require much knowledge of mathematics, ...
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English name and references for a combinatorial puzzle from Japan [closed]
I am looking for the name and references of the following puzzle.
There are n intersecting circles in a row.
At the center of the circle and at the intersection of the two circles, fill the numbers 1, ...
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The busy Star Guardian
On an infinite plane, the Prime Star has disintegrated into four constituent stars, the North Star, the South Star, the East Star and the West Star, each traveling at a constant speed of $1$ in their ...
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3D Edge matching puzzle generation
I have this weird idea for a puzzle/toy (or torture device, depending on how you look at it) I've been trying to make for years now.
I happen to be worse at this kind of math as I thought; and I'd be ...
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Russell's definite description and vacuous truth: a puzzle? [closed]
According to Russell's definite description theory, "The present King of France is bald" is a false statement. However, since for any property $P$, $P$ is true for the elements of the empty ...
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Partitioning a set of consecutive nonnegative integers into distinct pairs
Let us have a set of $k$ consecutive natural numbers $2,3,\ldots, k+1$, $k$ even. In addition, we are given a set of $m=\frac{k}{2}$ 'differences' from one among the $k$ numbers $1,2,\ldots, k$.
My ...
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Does Chu and Hough's solution to the mixing time of the 15-puzzle carry over to the Rubik's cube?
In his 1988 book Group Representations in Probability and Statistics , Diaconis considers mixing times of the 15-puzzle. He states:
Here is a simplified version: Consider the blank as a $16$th block,...
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Constructing a vector consisting of nonnegative entries
Consider constructing a vector $v=(a_1,a_2,\ldots,a_n)$ consisting of nonnegative integers such that $a_1=1$ and, if $a_j$'s are nonzero, then $a_j\equiv a_{n-j+2}+j-1 \pmod m\ \forall 1<j\le\frac{...
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Spread of a disease on a modular chessboard (torus) - lower bound
I learned about the following result from one of Peter Winkler's books:
It is impossible to infect the entire $n\times n$ chessboard (usual chessboard) starting from fewer than $n$ infected cells.
The ...
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Irreversible chess
Suppose we play a chess-variant, where any finite number of pieces are allowed, and the board is as large as we wish, but only two kings in total. And there is no 50 move-rule, no castling and no ...
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How many unit squares can you pack into a rectangle with nearly integer side lengths?
Earlier today, somebody asked what looks like a homework problem, but admits the following reading which I think is interesting:
Suppose $a_1,\dots, a_n$ are positive integers, and $\varepsilon$ is ...
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Number of 5x5 matrix permutations without repetitions in rows or columns
Context
In the boardgame Azul, your goal is to complete as much as possible of a $5\times5$ board by placing 25 tiles of 5 different colours (5 tiles of each colour) so that no colour appears twice in ...
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Maximum number of tuples from $n$ numbers such that no pair is repeated [duplicate]
What is the maximum number of $k$-tuples($3\le k\le n$) of $n$ numbers such that no pair is repeated in any of the tuples?
The maximum of number of $k$-tuples occur when $k=\lfloor\frac{n}{2}\rfloor$ ...
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Identifying poisoned wines
The standard version of this puzzle is as follows: you have $1000$ bottles of wine, one of which is poisoned. You also have a supply of rats (say). You want to determine which bottle is the poisoned ...
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1
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Circular track riddle
I'm puzzled by the following riddle, which seems easy at first, but turns out to be more complex than it looks. I would like to go to the bottom of it, and could not find references online.
The riddle
...
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Reconstruction puzzles
[Added: This is a follow-up of an earlier post.]
Consider the following "reconstruction puzzle", stated informally:
Given a concrete poset, e.g. the poset of undirected unlabeled finite graphs ...
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Sum and Product game
Two perfect logicians Steve and Pete, who have never met, before are imprisoned by an eccentric villain. "I have two positive integer numbers x and y" he says to them. "I will tell Steve the sum x+y, ...
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The lion and the zebras
The lion plays a deadly game against a group of $N$ zebras that takes place in the steppe (= an infinite plane). The lion starts in the origin with coordinates $(0,0)$, while the $N$ zebras may ...
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Bike lock graph
Motivation. I have a bike lock with 4 dials, and I was wondering whether I can reach any combination by always turning a fixed number $k$, say $k=2$, of the dials, by $1$ position, instead of just ...
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Bike lock puzzle
I was wondering this when using my bike lock, a combination lock with four dials, each of which has ten digits (0-9) on it in numerical order.
Suppose a bicyclist decides that, from now on, after ...
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Guessing the number of other $1$'s in a binary sequence
I have posed the following question on math.stackexchange.com but have not received an answer. So I would like to seek experts' opinion here.
Consider the set of all binary sequence of length $n+1$, $...
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Given $N$ integers on a circle, how to choose them in pairs to obtain minimum sum?
(Added by YCor 2019 July 7): it has been mentioned in the comments that this is part of a contest "Circular merging, July Challenge 2019 Division 1", where an equivalent question (just more clearly ...
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cube + cube + cube = cube
The following identity is a bit isolated in the arithmetic of natural integers
$$3^3+4^3+5^3=6^3.$$
Let $K_6$ be a cube whose side has length $6$. We view it as the union of $216$ elementary unit ...
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Guessing each other's coins
I recently thought about the following game (has it been considered before?).
Alice and Bob collaborate. Alice observes a sequence of independent unbiased random bits $(A_n)$, and then chooses an ...
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Lower bound on the number of solutions of N-queens problem
The OEIS lists the number of solutions of N-queens problem
(Number of ways of placing n nonattacking queens on an n X n board). However, no formula is given. It is easy to observe that each number in ...
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Computational complexity of fractions multiplication puzzle
I developed a puzzle for which I am seeking an EFFICIENT algorithm (I searched Google but did not find this puzzle in the literature, ):
You have $k$ rationals, $n_1/d_1, n_2/d_2, ..., n_k/d_k$.
...
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Math puzzles for dinner [closed]
You're hanging out with a bunch of other mathematicians - you go out to dinner, you're on the train, you're at a department tea, et cetera. Someone says something like "A group of 100 people at a ...
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