This tag is meant for questions about the mathematical principles behind games, riddles, or their possible solutions. If the answer is known to you please do not use this tag to "riddle" other users, but rather to ask about the correctness of a possible solution or ways to extend and improve an ...

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0
votes
1answer
27 views

Finding formula [on hold]

X Y Z Answer 8 2 4 0.5 8 2 2 0 8 2 8 1 My professor gave this as a sort of riddle to figure out, and it's ...
0
votes
1answer
28 views

infinite square grid of resistors

Given an infinite, 2-d, square grid of 1 Ohm resistors, what is the resistance between two adjacent nodes? (Something like a very large window screen, where the wires have finite resistance, but no ...
-2
votes
0answers
40 views

Next number in the sequence 19, 10,11, 18, 38,? [on hold]

What is the next number in the sequence 19, 10, 11, 18, 38 ? I received this image in a WhatsApp group. I don't know the book from which it is taken. It is question 140 of the image
3
votes
2answers
115 views

Math Snake Puzzle

A colleague recently showed me the following puzzle game and I'm interested in how this can be solved. I thought it would be a good talking point for you guys as well :) A detailed description of ...
0
votes
1answer
46 views

Work and efficiency puzzle

There are $2$ people $A$ and $B$. $A$ requires $a\;$ days to complete certain amount of work and $B$ requires $b\;$ days to complete the same amount of work. If $A$ begins the work a day before $B$ ...
-5
votes
1answer
57 views

What would be the solution to this logic puzzle? [on hold]

This is the puzzle I am having trouble in understanding Also, do explain me the question along with the answer. Thank You
4
votes
4answers
364 views

Find the sum of angles without trigonometry?

I have found the sum it's $180$ but using right triangle and sine theorem.
0
votes
0answers
31 views

Maximum length sequence with negative and positive subsequences

From ' mathematical puzzles' By Peter Winkler: " At the stockholders' meeting the CEO presents month-by-month profits and losses and declares : ' Since the last meeting we have made a profit in ...
4
votes
2answers
127 views

Find $I$ in $\frac{\overline{SIX}}{\overline{NINE}}=\frac23$

In $\frac{\overline{SIX}}{\overline{NINE}}=\frac23$ every letter denotes a UNIQUE digit,find $I$. Expanding the fraction in base $10$ we have: $300S+30I+3X=2020N+200I+2E$ , but this doesn't ...
0
votes
1answer
50 views

A cool number-theoretic puzzle in IMAT: find the last digit

This test is from IMAT 2015 (International Medical Admission Test): When I made a hotel reservation online yesterday I was given an $8$ digit booking reference which contained no zeros. It did, ...
2
votes
1answer
64 views

Circle Puzzle Geometry

Two friends are playing a game. One friend stands in the middle of a circle radius 100m. His objective is to leave the circle. He may take one step at a time, distance 1m, in any direction. However, ...
1
vote
2answers
70 views

Nice explanation for simple puzzle

There is a simple game with coins that goes as follows. You have $x$ coins and two players who take turns. Each player can either remove one or two coins. The winner is the person who removes the ...
0
votes
1answer
21 views

Devising an $n$-place mastermind variation algorithm

A few days ago I came across such a problem at the contest my uni was holding: Given the history of guesses in a mastermind game using digits instead of colors in a form of pairs $(x, y)$ where $...
3
votes
1answer
39 views

How to tame a Rechenschlange

I found the following problem, called Rechenschlange (literal translation: calculation snake) in a German puzzle calendar: Fill the blanks with the numbers 1-9. Each number must only appear once. ...
4
votes
2answers
49 views

55 Coins- / Young-Diagram Rearrangment-Riddle

this has been a riddle to difficult for me to understand the solution some year ago. Even though the riddle seems really easy. You have got 55 coins. Someone builds an arbitrary number m of stacks ...
-1
votes
1answer
31 views

Two guys pick from $n$ stones, the numbers of stones they can pick lie in a given set S. When the guy who pick first will win?

Alice and Bob take turns to pick stones from a pile of $n$ stones. Each number of stones they pick must lie in a given finite set $S\subset \mathbb{N}$. Who cannot pick will lose. If Alice picks first,...
1
vote
1answer
45 views

finding the missing number by pattern

In this riddle you need to find a pattern between every couple of numbers. Given numbers $5$ and $10$ there is a pattern like in the numbers $10$ and $3$. Given numbers $10$ and $15$ there is a ...
1
vote
1answer
35 views

Create a strictly increasing sequence following criterias

Problem Let y be a sequence of real numbers (of length $n$) bounded in the range [0,1]. I am trying to calculate the sequence x ...
0
votes
2answers
38 views

Do these infinite expressions have a meaning?

While playing with expressions, I came up to the following "infinite sums". I haven't seen them anywhere else but maybe I didn't look long enough. Find the values of $s$ and $t$. $$s=\sum\nolimits_{1}^...
-1
votes
2answers
84 views

Math's puzzle school problem

I got this weird homework situation and i can't find out what the answer is. I got to find out how to get $828$ using the numbers $8, 6, 8, 3, 75$ and $9$. Moreover, I can use all the operators $*, -,...
20
votes
6answers
707 views

Non-trivial “I know what number you're thinking of”

Consider the following 'trick' (WARNING: very lame) Think of a number. Multiply this number by two. Add four. Divide the number by two. Subtract the number you were originally thinking of. I guess ...
4
votes
2answers
57 views

Meeting probability of two bankers: uniform distribution puzzle

Two bankers each arrive at the station at some random time between 5PM and 6PM (arrival time for each of them is uniformly distributed). They stay exactly five minutes and then leave. What is the ...
4
votes
7answers
146 views

A logic riddle from “The Lady or the Tiger?” by Raymond Smullyan

Just to clarify, Case 3 and Case 4 must have flawed reasoning in order to reconcile my proof with the author's. I have been having a problem with a particular riddle from Raymond Smullyan and I can't ...
2
votes
2answers
42 views

Awesome riddle including independence and exponential distribution [closed]

The life cycles of 3 devices $A, B$ and $C$ are independent and exponentially distributed with parameters $\alpha,\beta,\gamma$. These three devices form a system that fails if not only device A fails ...
6
votes
1answer
233 views

Why was I wrong about the monster-gem riddler

Every week I like to do the fivethirtyeight.com Riddler, an interesting and pleasantly challenging (at least for me) weekly math puzzle which comes out Fridays, with the answer and explanation to the ...
12
votes
1answer
231 views

Doing a magic trick with limited memory (from a problem solving course)

I got the following question in a problem solving course: There are four different objects lying on places 1, 2, 3, 4. A magician closes his eyes and someone from the audience comes. He switches ...
1
vote
0answers
75 views

Cat and a mouse on a circle

I hope this is the right plcae to post it as I'm not sure if the solution is mathematical. I saw this riddle on a board at the university and it seems that there's something I'm missing. It goes as ...
3
votes
2answers
96 views

2048 Logic Puzzle

I thought up this logic problem related to the 2048 game. If all 16 tiles on a 2048 board all had the value 1024, how many ways are there to get to the 2048 tile? Here is what I am talking about in an ...
0
votes
1answer
57 views

Proof of coin and bag problem

There are 5 bags labeled 1 to 5. All the coins in a given bag have the same weight. Some bags have coins of weight 10 gm, others have coins of weight 11 gm. I pick 1, 2, 4, 8, 16 coins respectively ...
10
votes
2answers
152 views

5x5 Bingo Puzzle [Logical thinking problem]

5 people participate in a custom game. They are given blank cards, in which they have to fill numbers from 1-25 in a 5x5 table. Each card must contain all the numbers from 1-25 without repetition. The ...
25
votes
3answers
759 views

Sudoku with special properties

Sudoku is a puzzle, with the objective is to fill a 9×9 grid with digits so that each column, each row, and each of the nine 3×3 sub-grids that compose the grid (also "sudoku-blocks") contains all of ...
1
vote
0answers
63 views

Twisty Puzzle Solving Program

I'm writing a program to help me solve a twisty puzzle. In this case it's the face-turning octahedron. I'm representing the puzzle as a group with face twists as generators. The facelets are in a list ...
1
vote
0answers
86 views

Position games: how to fill a matrix with dominos? [duplicate]

Dominos of size $2 × 1$ can be placed on a $m × n$ board so as to cover two squares exactly. Two players alternate placing dominos. The first one who is unable to place a domino is the loser. I can ...
-1
votes
2answers
75 views

Random Room changing in the Hilbert hotel. [closed]

Let's say you have a Hilbert's grand hotel full occupancy. Assign each occupant a new room select randomly without regard to whether the room is assigned to someone. i.e. empty rooms, multiple ...
0
votes
0answers
67 views

Generalization of classic 3 roll die game to $n$ rolls

I am trying to generalize the following well-known 3 roll die problem: "We roll a single die no more than 3 times. We can stop immediately after the first roll, immediately after the second roll, or ...
6
votes
2answers
97 views

Monty Hall Problem extended

After seeing the popularity of the standard $3$ door problem, Monty thought to put a twist in the story. There are $N$ doors, $1$ car, $N-1$ goats. We need to choose any one of the doors. After we ...
0
votes
1answer
26 views

How to decide what numbers to show in a sudoku grid so that it's solvable?

Let's assume I've generated, from an empty board, a complete and valid sudoku board by some means. Borrowing from this question, let's say that board is: ...
4
votes
1answer
39 views

When are all pairwise sums consecutive?

What finite ascending sequences of integers $(a_1, \cdots, a_n)$, with $a_1 = 0$, are such that the sequence obtained by sorting all the pairwise sums $a_i + a_j\;\;(j > i)$ consists of ${n \choose ...
0
votes
0answers
48 views

An Interesting Variation to the “Pebbling a Checkerboard” Puzzle

Pebbling a Checkerboard (or chess board) was a puzzle proposed by Maxim Kontsevich in 1985, which was very interesting and fun to try, and you can find a great video on it at: https://www.youtube.com/...
0
votes
0answers
73 views

100 people standing in a circle.

I've got this problem on my Graph algorithms exam and I still can't solve it!Here is the problem: At first there are 100 people sitting at a round table and neither one is enemies with their neighbor....
0
votes
0answers
29 views

Convert Levenshtein Distance to percents

This is my first post here so please bare with me. I would like to ask if is possible to convert Levenshtein Distance to percents? There is similar question on StackOverflow which does have several ...
0
votes
1answer
41 views

Does the first player have a winning strategy?

Two players play a game where they alternatively cross out a number from the numbers written on the board ($1-21$). They stop when two numbers are remaining. If thie sum of these two numbers is ...
1
vote
2answers
55 views

Optimization with a Probability

Imagine two points in $ℝ^2$ at $(-1, 0)$ and $(1, 0)$. You would like to walk from one point to the next in the shortest distance possible. However, there is a line segment coming from the origin to a ...
2
votes
1answer
54 views

A puzzle concerning the axiom of choice and the reals

Recently I was told the following riddle: Let $A=(a_1,...a_n,...a_{2n},a_{2n+1})$ a 2n+1-tuple of real numbers with the following property: Whatever number $a_i$ is removed from $A$ the remaining 2n ...
21
votes
0answers
165 views

Painting the plane red and blue: Is it possible for each unit circumference to contain exactly $n$ blue points?

I recently stumbled upon the following problem: Consider the plane: You may color each point either red or blue. Is there a way to color it such that each unit circumference (centred anywhere) ...
4
votes
3answers
64 views

Time-and-Work and Motorcycle Tyres

A problem about motorcycle tyres, related to Time-and-Work or rate-of-work methods. This is not a homework question, nor, as far as I know, a contest question. It is intended as a challenge for Year ...
1
vote
0answers
73 views

Will the boy outwit the teacher in this way? [duplicate]

In the book, Solving Mathematical Problems: A personal perspective (written by Terry Tao), he discusses a problem named (on Analytic Geometry Chapter, page 79): Problem 5.4 (Taylor 1989, p. 34, Q2)...
6
votes
0answers
155 views

Separating Heavier from the Lighter Balls

This was posted Here and received a good answer, solving the general questions in either $n$ or $n+1$ moves, which is by just half a move on average "less good" than my manual solutions here. ...
1
vote
6answers
299 views

What's the solution to this puzzle? [closed]

I saw this on Instagram with no solution and was wondering what the answer is. I got $33$. $$1+4=5$$ $$2+5=12$$ $$3+6=21$$ $$8+11=?$$