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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-3
votes
1answer
115 views

SEVEN - NINE= EIGHT [on hold]

Things are not always what they seem. What is true from one point of view may be false from another and vice-versa, and here is a puzzle to prove it. Despite the fact that every arithmetic teacher in ...
0
votes
0answers
63 views

Logic puzzle of two numbers

The puzzle goes like this.. ...
10
votes
11answers
160 views

Get the numbers from (0-30) by using the number $2$ four times

How can I get the numbers from (0-30) by using the number $2$ four times.Use any common mathematical function and the (+,-,*,/,^) I tried to solve this puzzle, but I couldn't solve it completely. Some ...
5
votes
2answers
109 views

Prisoners Problem

We have an infinite number of prisoners enumerated $\{1, 2, \dots\}$, and on each prisoner there is a hat of either blue or red color. The $n$th prisoner sees the hats of prisoners $\{n+1, n+2, ...
1
vote
1answer
35 views

Probability puzzle : Expected no. of coins in the smaller pot

There are two pots of coins having size m & n. A new coin is thrown and goes to 1st pot with probability m/(m+n) and to 2nd pot with probability n/(m+n). We start with both pots of size 1 & 1 ...
0
votes
2answers
55 views

Lights Out with custom rules set

I'm trying to understand how to use linear algebra to solve a custom Lights Out puzzle with the following rules: There are 8 lights, all the lights are off at the starting point, I need to turn on ...
1
vote
1answer
32 views

Probability : Maximize the expected payoff

Given $2$ random variables $X, Y$ that take integer values with uniform distribution from $0$ to $100$. You play a game in which a random value of $x$ comes first & you have to decide if the ...
0
votes
1answer
31 views

How to count jigsaw puzzle height and width in pieces.

How can I calculate jigsaw puzzle dimensions (height & width) in puzzle pieces? I have a puzzle which consist of $3,000$ pieces (the paper inside the box says that because of technical reasons ...
5
votes
4answers
664 views

A maths number puzzle

We have these digits : $1,2,3,4,5,6,7,8,9$. Using these digits, we have to make two numbers such that their product must be as large as possible. We have to use all digits only once. I did ...
1
vote
1answer
37 views

What is the relation between these numbers? [closed]

This in an IQ question. I need to find relation between these: I appreciate if anyone can help to find relation between these numbers. By the way the answer is A (number 3) from this link and then ...
3
votes
1answer
34 views

Four Isosceles Trapezoids

Suppose we have four isosceles triangles with the same area, which must some whole number less than $29$. Denote the the lower base and upper base of the $i$-th triangle with $y_i$ and $x_i$, ...
3
votes
1answer
39 views

Find a seven digit number which describes itself

Find a seven digit number which describes itself. The first digit is the number of zeros in the number. The second digit is the number of ones in the number, etc. For example, in the number 21200, ...
2
votes
2answers
44 views

What is the probability for a wood stick of real number length breaking in three piece that can forming precisely a triangle?

What is the probability for a wood stick of any real number length breaking in three piece that can forming precisely a triangle without any extra segment extend from the side of the triangle? My ...
18
votes
4answers
354 views

How many $\mathbb R$s must a Mathematician walk down?

A mathematician is lost on the complex plane. He knows neither his position nor the direction he is facing. He wants to return to the main road, a strip of width $1$ around the real axis (that is, ...
0
votes
1answer
63 views

Probability Paradoxes that Puzzle Professors.

There is a class of probability puzzles that includes Monty Hall/Three Prisoners, Three Cards/Pancakes, Two Children/Boy or Girl, their common antecedent Bertrand's Box Paradox, and (a more ...
4
votes
3answers
90 views

Using up letters on a refrigerator is NP-complete

You spend some time with your preschool-age daughter trying to use up all of the magnet letters on the refrigerator to spell words that she knows. Formally, you have a set of letters and you are ...
15
votes
5answers
1k views

Puzzle of gold coins in the bag

At the end of Probability class, our professor gave us the following puzzle: There are 100 bags each with 100 coins, but only one of these bags has gold coins in it. The gold coin has weight of ...
0
votes
1answer
51 views

Cops and robbers in a square

A problem from Moscow Mathematical Olympiad in 1973. goes like this: At the center of a square stands a cop and at one of the square’s vertices stands a robber. The Rule allows the cop to run ...
2
votes
0answers
28 views

determine the number thought of

Ten people are seated around a circular table. Each of the ten people thinks of a number and whispers it to his/her two neighbours. Then these ten people announce the average of the two numbers they ...
0
votes
2answers
42 views

how many days at work?

There are scheduled buses traveling between Somewhere and Nowhere. There is only one road between the two villages, so the buses take this road. From both villages the buses leave for the other ...
2
votes
1answer
34 views

counting hands shake

Mr. and Mrs. Brown gave a party for their friends they have not seen for a long time. Three couples came. During the party, some of the people were so happy to see each other again, that they even ...
0
votes
1answer
14 views

Show that an integer in an odd base system is odd in the base 10 system…

Show that an integer in an odd base system is odd in the base 10 system if and only if it has an odd number of odd digits. I have an idea of how the proof should go in my head, but how do I express ...
4
votes
4answers
71 views

Find a positive integer with prime factors of at most 2, 3, 5, 7 and ends in the digits 11

Does there exist a positive integer whose prime factors include at most 2, 3, 5, and 7, and ends in the digits 11? If so find the smallest positive integer. If not, show why none exists. My professor ...
3
votes
2answers
90 views

how to solve triangles count puzzle

Below is a puzzle of counting triangles.How to solve such puzzle ? source: http://gpuzzles.com/mind-teasers/how-many-triangles-challenge/?source=stackmath
1
vote
2answers
54 views

Counting problem about pirates and gold coins [duplicate]

Five pirates find a cache of 500 gold coins. They decide that the shortest pirate will serve as the bursar and determine a distribution of the coins however he sees fit, and then they all will vote. ...
0
votes
3answers
59 views

Recovering the original values from given information.

We have some N numbers[1..N] and N students. Originally we assign each number to single student. Call this assignment as the initial state of the assignments. Instance of assignment is described as ...
3
votes
3answers
80 views

Proof of 3-chain subsequence problem from assignment 2 of MIT OCW 6.042

I was trying to solve this question but stuck with how do I prove it so. I do have the intuition but how to prove it? Here is the link to the page and this one is the problem 1!! ...
1
vote
4answers
54 views

How many faces does the resulting polyhedron have?

Take a regular tetrahedron of edge one. Also take a square-based pyramid, whose edges are all one (therefore the side faces are equilateral triangles of same size as the faces of the tetrahedron). ...
1
vote
0answers
29 views

3D Extension of a Fun Geometric Series Puzzle

After being inspired by this question, and in particular Semiclassical's excellent response and generalisation, I thought of another generalisation to a 3-dimensional plane.: Suppose you start at ...
2
votes
1answer
27 views

Calculate percentage between two sensorvalues

I've got two distance sensors on the sides of a car, and I'm trying to come up with a formula that will attempt to put the car so that it has an equal distance on both sides. There is an IR sensor on ...
1
vote
1answer
37 views

The Special Table

Consider a $n\times n$ table which is filled with numbers $1,2,3,...,n^2$ (in no particular order).We'd call such table "Special" if the sum of each column and each row and each diameter is a constant ...
2
votes
1answer
34 views

Forming peaceful teams

Let us have set of $n=mk$ people that have to be divided into $m$ teams, each with $k$ members. Let us denote the set of the people $S=\{1,2,\dots,n\}$ and the teams $S_i\subset S$. We consider a ...
0
votes
1answer
47 views

Placing bricks on Board

Situation: I have a $8\times 8$ board (sic), but two squares from it's one diagonal are removed (Black colored squares are removed) I'm given with plenty of(Rectangular) bricks having dimensions ...
1
vote
2answers
61 views

Sand-Timer egg boiling

You need to boil an egg. For this task you have to following items: An egg. a pot, filled with boiling water a spoon (to take the egg in and out of the pot) Two Sand-Timers (with amount of time as ...
1
vote
1answer
67 views

$a^4+b^2+c^2=2014$

Word for word: The equation $a^4+b^2+c^2=2014$ has a unique integer solution in positive integers. For this solution, find $a+b+c$. A. 56 B. 58 C. 60 D. 62 E. 64 This is a tricky one. And ...
0
votes
1answer
46 views

Solve this puzzle by gpuzzles

you and Me are playing bets. I take $10 from you and that begins our game. I shuffle the deck of cards (52 cards normal deck) and take out four random cards out of it. Now I place the cards in front ...
0
votes
0answers
38 views

Does there exist a covering of a square?

Consider a square of length $ S \in \mathbb{N} $ and a given set $ M $ of $ t \in \mathbb{N} $ smaller squares of lengths $ s_1,\ldots,s_t \in \mathbb{N} $. Are there any conditions, so that I can ...
2
votes
1answer
44 views

Best score in this puzzle

I want to maximise the score of the following table, choosing one item from each column/row, so no two items are on the same row or column. Score to maximise is just adding all the choices together. ...
4
votes
3answers
98 views

Puzzle: “Yes colour of my hat is white.”

There are $n$ people in room each being put on hat from amongest at least $n$ white hats and $n-1$ black hats. They stand in a queue, so that everyone can see the colour of the hat of the person ...
2
votes
2answers
43 views

Interview question - numbered tiles

Ok, this interview question interested me and I would love to see an explanation! There are some tiles: 1, 1, 2, 2, 3, 3 They must be placed in a straight line, such that there is one tile between ...
20
votes
3answers
489 views

Math puzzle: 10 digit strings generations

There was a question in a math competition that I attended last year. At the end of competition, I realized that my answer was wrong for the question below and I have never been able to figure out how ...
3
votes
2answers
85 views

Who is the last person?

twenty five people are standing in a circle. starting with person 1, they count off from 1 to 7 and then start over with 1. each person who says "7" drops out of the circle. who is the last person ...
77
votes
10answers
9k views

Mathematician vs. Computer: A Game

A mathematician and a computer are playing a game: First, the mathematician chooses an integer from the range $2,...,1000$. Then, the computer chooses an integer uniformly at random from the same ...
0
votes
0answers
42 views

Alternative numbering system?

The markings below are on the right of page at http://lyca.com/story/ It seems pretty clear they are part of a numbering scheme since they appear at mostly regular intervals. This may be related to a ...
0
votes
1answer
29 views

Game of Life receptor

I am looking for an interesting structure in the game of life. If left alone, it shouldn't expand a lot(Still lifes or oscillators are allowed), but if we add an life somewhere, it launches an ...
14
votes
3answers
3k views

Largest prime number with all digits different

What is the largest prime with distinct digits? (It is certainly less than ten digits long.Can you explain it why?
1
vote
2answers
115 views

Two math professors problem

My friend asks me a question from internet. The question is as follows Two math professors, professor Uno and professor Dos, play chess at the park while reminiscing about their past. Prof. ...
1
vote
0answers
28 views

how to find if a number has a representation in a powerbase format?

I better explain this problem with an example, $100$ would be represented as $983$ because $9^1 + 8^2 + 3^3$ is one hundred. So how to find the relation between the number $n$ and numbers that can be ...
1
vote
1answer
54 views

Why is the “rational” solution to the Traveler's Dilemma 2?

Traveler's Dilemma An airline loses two suitcases belonging to two different travelers. Both suitcases happen to be identical and contain identical items. An airline manager tasked to settle the ...
0
votes
2answers
133 views

Pigeon hole principle based puzzle question

A card-board box contains 12 pairs each of three different types of hand gloves used by batsman in cricket. They are separated into single units of gloves and all mixed. you can not see the gloves ...