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
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3answers
87 views

walking along the number line

Suppose you start walking along the number line from $0$ to $100$, moving $1$ position to the right in each step. There are some shortcuts $(i,j)$ where $i,j\in[0,100]$ and $i<j$. If you step on $i$...
27
votes
5answers
404k views

How many squares actually ARE in this picture? Is this a trick question with no right answer?

This is one of those popular pictures on sites like Facebook. I always see a huge variation of answers such as $8, 9, 16, 17, 24, 28, 30, 40, 41, 52,$ etc., yet I've never seen a definitive answer on ...
2
votes
3answers
140 views

Is this Chinese card game solved?

There is a card game here in China, use a standard 52 card deck of cards. Draw four cards and use any elementary operators $(+,-,\times, \div)$, and only use each card value once to get a result of ...
0
votes
2answers
546 views

How much the shopkeeper loses? [duplicate]

I struck with this tricky math question A girl went to a shop and bought a Rs.$200$ show piece. She gave a Rs.$1000$ note to shopkeeper. Shopkeeper didn't have any change so he went outside and ...
2
votes
3answers
341 views

An algorithm for solving this puzzle

The puzzle goes like this: There is a $n\times n$ - board with each cell containing a whole number. Let's call this the matrix $A$ and denote its elements by $a_{ij} \in \mathbb Z$. The cells can be ...
6
votes
4answers
184 views

A puzzle that came when I am half awake

When I am about to wake up in the morning, a puzzle crept into my mind.It is when $\sqrt{a}$ and $\sqrt{b}$ are both non-integers where $a,b$ are positive integers is it possible for $\sqrt{ab}$ to ...
4
votes
1answer
173 views

How many answers to this combinatorial puzzle?

Take a square. How many ways are there to draw or not draw a line from the center to each of its sides? 16, of course. Here are all the different squares: Now, how many ways are there to put ...
0
votes
1answer
27 views

Condition for L and R to make the below scenario true?

You are a given a number N. N <= 10 ^ 9 . You are given a range of numbers L and R . ...
1
vote
2answers
105 views

Ball bouncing in a box, will it meet a vertex.

I have no idea upon how to solve this: A box 5cm by 3cm with a ball projected from a vertex at 45 degree angle, it reflexes at a 45 degree angle and keeps reflecting at a 45 degree angle. Will it ...
2
votes
2answers
74 views

Show that 4*AB=CAB is not possible

Show that 4*AB=CAB is not possible.Each letter denotes a single digit.It could be noted that since LHS is a multiple of 4,thus RHS would also be a multiple of 4.That's all i conclude yet...
4
votes
5answers
2k views

A three-way duel (probability puzzle)

This puzzle is taken from Mathematical Puzzles: A Connoisseur's Collection [Peter Winkler]. I don't understand the solution. Alice, Bob, and Carol arrange a three-way duel. Alice is a poor shot, ...
3
votes
1answer
99 views

Dropping a penny from a tall buidling

If a penny is dropped from a tall building how long does it take for it to hit the ground ? If dropping the penny from a building that is L1 feet tall takes S1 seconds I guess dropping from a ...
3
votes
3answers
102 views

To maximise my chance of winning one prize should I put all my entries in a single draw?

Every week there's a prize draw. It's free to enter using the code from a soup tin lid. You can enter as many times as you like during the week until Monday's draw and then it starts all over. The ...
-1
votes
3answers
130 views

logical negation of a statement: any mammal that has long ears has at least [closed]

Write the negation of the following statement: Any mammal that has long ears has at least one of its predators with yellow eyes having all of its cubs that cannot fly. Write it in the logical ...
1
vote
0answers
74 views

When does a ball in a game of brick breaker never hit the remaining breaks?

I have a block size 2N*2N and some squares are filled with bricks and some aren't. I have a ball that travels distance 1 in the x and y direction and bounces off with perpendicular direction if it ...
2
votes
2answers
212 views

Problem about points on an equilateral triangle [duplicate]

Suppose that $A$, $B$, and $C$ are three points in a plane, such that $AB = AC = BC = 1$. At each point in time, $A$ is moving toward $B$, $B$ is moving toward $C$, and $C$ is moving towards $A$, all ...
7
votes
2answers
356 views

Fun math puzzles for kids

I'm trying to find fun puzzles for younger people (7 years of age and up). I've browsed the internet, searched through math books etc but haven't really found a stellar puzzle. I realize that ...
90
votes
12answers
10k views

Logic puzzle: Which octopus is telling the truth?

King Octopus has servants with six, seven, or eight legs. The servants with seven legs always lie, but the servants with either six or eight legs always tell the truth. One day, four servants met. ...
0
votes
2answers
75 views

Function to change inputs from 0.5 to 1, to 0 to 1

Let's say we have x, which is any decimal number between 0.5 and 1. What function can be applied to it such that an input of 0.5 equals 0 and input of 1 equals 1? ...
-1
votes
1answer
329 views

Puzzle: Trail a shape without overlapping lines

Here is a challenge a friend of mine came up with: Use a pen and recreate this shape. You can only draw 3 lines that can start anywhere and end anywhere. The lines cannot overlap at one point. ...
1
vote
1answer
246 views

How to solve for getting average of them

I am trying to solve this problem If x+y= 6, y+z= 7 , and x+z= 9 , what is the average of x , y and z ? Well how i am trying to do is getting the value of 'X' , '...
1
vote
1answer
373 views

How I got this answer

Well i am new to this forum but old to stack exchange but i don't know much about mathmatics tags so sorry for the wrong tags if any. I have a question, but i want to know how i got its answer as 'D' ...
0
votes
4answers
534 views

Odd one out questions

These are two questions given to a grade 5 student. I couldn't get a conclusive and compelling answer to any.
1
vote
6answers
4k views

Probability problem…

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2
votes
3answers
120 views

Average of the smaller of three random numbers from $0$ to $1$

A friend of mine claims he saw the following question on a math puzzle site:- What is the average of the smaller of three random numbers from $0$ to $1$? And they've given these options:- $A) \frac{2}{...
4
votes
1answer
361 views

A 5x5 board has 25 cells.The numbers $\{1,2,3,4,5\}$ are written on every row,every column and the two main diagonals.

A 5x5 board has $25$ cells. The numbers $\{1,2,3,4,5\}$ are written on every row,every column and the two main diagonals without any repetition. If the sum of the numbers of the diagonal below the ...
24
votes
4answers
1k views

Number of vectors so that no two subset sums are equal

Consider all $10$-tuple vectors each element of which is either $1$ or $0$. It is very easy to select a set $v_1,\dots,v_{10}= S$ of $10$ such vectors so that no two distinct subsets of vectors $S_1 \...
0
votes
1answer
31k views

I don't see the pattern.. does anyone understand this..? [duplicate]

Note.. the numbers are actually in a 7 x 6 grid.. graphics did not show here.. ...
0
votes
2answers
371 views

How to deduce this puzzle

Every station on the railway system sells tickets to every other station. Some new stations were added. 46 sets of additional sets of tickets were required. How many new stations have been added? How ...
3
votes
2answers
188 views

Number-Theoretic Coin Puzzle

There are three piles of coins. You are allowed to move coins from one pile to another, but only if the number of coins in the destination pile is doubled. For example, if the first pile has 6 coins ...
0
votes
1answer
3k views

How many triangle can be drawn with those points? [duplicate]

There are 7 points on the circumference of a circle.How many acute triangle can be drawn with those points. please help me to solve this problem.
2
votes
1answer
94 views

Maximal number of kings on a chessboard, but this time two can be adjacent.

How many kings can be placed on an $8 \times 8$ chessboard such that every king can capture (is adjacent to) at most one other king? I can do 26, but can not prove that this is optimal.
3
votes
0answers
209 views

Limits of infinite processes that terminate in finite time - checking my understanding?

I am a computer scientist by training, but have a fair amount of math background that I've picked up through classes, teaching, and general interest. A student of mine posed a question to me. I think ...
0
votes
1answer
46 views

Finding affiliation of a number to a finite number of sets of incremental numbers

I have different sets of incremental numbers starting from zero like this: $S_1=\{0,1,2,3\}$ $S_2=\{4,5,6,7\}$ $S_3=\{8,9,10,11\}$ Each set has the same cardinality. I want to know, given a ...
2
votes
1answer
5k views

The Blind Man and Coins Puzzle

There is a table on which, a number of coins are placed. You also know that there are as many coins with Heads up, as many coins with Tails up. You are blind folded and there is no way to determine ...
5
votes
1answer
633 views

The Fox And The Duck Puzzle

A duck, pursued by a fox, escapes to the center of a perfectly circular pond. The fox cannot swim, and the duck cannot take flight from the water. The fox is four times faster than the duck. Assuming ...
1
vote
2answers
169 views

Ant on a square [duplicate]

There is a square of side $1 m$ and an ant has to cross diagonally. However, it chooses to walk along the boundary so the distance covered by it is $2m$ and not $\sqrt{2} m$. This it does in two moves....
2
votes
1answer
399 views

Sangaku: Find the Radii of the Inner Circles

Sangaku (算額) are Japanese geometric puzzles written on wooden tablets over 150 years ago. There have been several previous puzzles, but I didn't see this one. Find the radii of the two inner circles ...
1
vote
2answers
960 views

Math Riddles #10 - Car Meter Riddle

Today my car meter reads as 72927 kms. I notes that this is a palindrome. How many minimum kms I need to travel so my car meter find another palindrome?
5
votes
7answers
2k views

3 trams are coming every 10, 15 and 15 minutes. On average, how long do I have to wait for any tram to come?

3 trams are coming to the stop every 10, 15 and 15 minutes. On average, how long do I have to wait for any tram to come? It's a practical problem, not some kind of a riddle for which I have a ...
1
vote
1answer
2k views

The 100 Coins Puzzle

There are 10 sets of 10 coins. You know how much the coins should weigh. You know all the coins in one set of ten are exactly a hundredth of an ounce off, making the entire set of ten coins a tenth of ...
1
vote
1answer
89 views

Maximum score for the game

Here is a game: There is a list of distinct numbers. At any round, a player arbitrarily chooses two numbers $a, b$ from the list and generates a new number $c$ by subtracting the smaller number from ...
1
vote
1answer
262 views

100 prisoners and a light bulb

I'm curious if there is a solution,however ineffective, for the puzzle when the prisoners do not know whether initially the bulb is on or off. Second, has several bulbs modification of the problem ...
0
votes
2answers
140 views

How many zeroes (at the end) will 10! have when written in base 3?

I can get the answer for the question by calculating 10! and then converting it to base 3 but is there a more logical point of view to this question which will mostly generalise the solution for this ...
5
votes
1answer
268 views

How many points you should draw in the square at least?

There is a square, which side length is $2$, To ensure there exists a triangle in the square, with an area less than $0.5$, how many points should you draw in the square at least. the goal is for all ...
6
votes
2answers
346 views

Relatively prime property verification

I am reading a computer science puzzles book. And I get the following question - "You have a five quart jug, a three quart jug and unlimited supply of water. How would you come up with exactly four ...
3
votes
1answer
186 views

Looking for a pattern in a math riddle

Looking to find a pattern but no idea how: $12\mathop{\square}21 = 86$, $13\mathop{\square}31 = 192$, $14\mathop{\square}58 = 389$, $14\mathop{\square}94 = \ ?$
2
votes
1answer
654 views

How to reason about disentanglement “tavern” puzzles?

It took me an embarrassingly long time to remove the ring from this rigid structure: What math could I use to solve similar puzzles? Topology and knot theory seem helpful, but I don't think they ...
0
votes
2answers
143 views

I have a button…(story problem)

Tom has a job. He is a button pusher. He works for 8 hours per day. his job at work is simply to push a button. He has some freedoms and some limitations. When he arrives to work each day he has 5 ...
3
votes
2answers
94 views

The king's reversal in the classical chess problem?

I was talking to my math teacher about the classical problem where the king loses a chess match against a peasent and he is asked to give him $2^n$ grains for the $n$'th square (where the squares are ...