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 ...

learn more… | top users | synonyms (1)

0
votes
1answer
74 views

Calculate Income Of the Month [Puzzle]

Mr. Jill requires Rs 6000 per month to maintain his family. He saves 20% of any amount that he earns above Rs. 6000 but below Rs 7000 in a month. He saves 30% of amount that he earns above Rs 7000 but ...
0
votes
1answer
310 views

Math Brain Teaser! Can't solve, please help! [closed]

The sum of face values of two coins is twice the difference of the two. Find them. My math professor gave us a brain teaser, but I am extremely confused on how to solve it. I am aware that it might ...
3
votes
1answer
193 views

Riddle about dog running in company of soliders

A group of soldiers march together straight in square formation $50 \times 50$ meters. There is the dog at the back of the formation. Dog starts to run towards the first line of soldiers and then when ...
0
votes
2answers
135 views

Riddle about ant going through self extendible string

Ant stands at the end of a rubber string which has 1km of length. Ant starts going to the other end at speed 1cm/s. Every second the string becomes 1km longer. For readers from countries where ...
2
votes
3answers
2k views

Crossword puzzle- Crossnumber puzzle

The puzzle below is a cross number puzzle, similar to a crossword puzzle except that the entries are numbers. Enter one digit per square. The thick heavy line is a separator. ACROSS: a. A prime ...
1
vote
0answers
288 views

Wedding Vows puzzle

My father came up with a puzzle and dared me to solve it. I could solve it by trial and error, but I rather want to solve it mathematically. It is the so called "Wedding Vows puzzle" where you have to ...
4
votes
7answers
371 views

How can I formulate the two guards puzzle to disallow references to the other guard?

An old logic puzzle goes as follows: There is a gate with two doors, each leading to a different city – Tannenbaum or Belvedere. You wish to get to Tannenbaum, but you do not know which of ...
2
votes
1answer
96 views

Puzzle : cable in the field

Here is an interesting puzzle taken from mathproblems.info: There is a straight cable buried under a unit square field. You must dig one or >more ditches to locate the buried cable. Where should ...
1
vote
2answers
206 views

Riddle about number of children Mr. A,B,C have

I have a riddle and I am stuck with it second day. Mr. A,B,C have in total 6 children: 5 sons and 1 daughter. John has one child more than Mr.B. Thomas has the same number of childrean as Peter and ...
15
votes
2answers
2k views

Is the game 2048 always solveable?

Games got me on math. I always want to play best. I don't know how to answer my question. My question is : How to show that the game 2048 is (always) solvable>? Is there any method other than ...
4
votes
1answer
58 views

Constructing of sequences with steps already “existing” in sequence

Sequence $\{a_k\}$ is built according to next rule: $$ a_0=0;\\ a_1=1;\\ \forall n\in \mathbb{N} ~ \exists i,j ~ (0\leqslant i<j\leqslant n),\mbox{ so that } a_{n+1}-a_{n} = a_j-a_i. $$ Conjecture:...
35
votes
9answers
74k views

Maximum board position in 2048 game

A game called 2048 is making rounds on social media. I am trying to determine the maximum score attainable for this game. Let's assume WLOG that only 2s are returned (if 4s are possible the max score ...
1
vote
3answers
177 views

What is the next number? [closed]

What is the next number in the following set ? $$1,11,21,1211,111221, \ldots$$
23
votes
9answers
5k views

Is Lewis Carroll's reasoning correct?

A bag contains 2 counters, as to which nothing is known except that each is either black or white. Ascertain their colours without taking them out of the bag. Carroll's solution: One is black, and ...
-1
votes
1answer
154 views

Question on Speed and Distance

X, Y and Z move along a circular path of length 1.2 km with speeds of 6 km/h, 8 km/h and 9 km/h respectively. X and Y move in the same direction but Z moves in opposite direction. If they all start at ...
6
votes
5answers
3k views

Bringing the fox, the goose and the cereal across the river unharmed

Solve puzzle algebraically? I can't come up elegant and algebraical solution. There are man, fox, goose, and cereals. If the man is not beside the fox, the fox will eat the goose. If the man is ...
3
votes
2answers
230 views

Fisherman riddle: Combining probabilities

This is more a probabilities problem than a riddle. The riddle is: I am in a village, where a fisherman lives. The fisherman tells me that there is a 70% possibility that it will rain tomorrow. I ...
2
votes
1answer
121 views

Problem of the Week! [duplicate]

This week in Algebra II we are studying the Hanoi tower's. Our assignment was to find what type of formula would give the number of moves it would take to solve the puzzle. After using a T-chart (...
3
votes
3answers
245 views

solve the puzzle how many liars?

Each boy in a group of $20$ boys either always tells thuth or always tells a lie. These boys are sitting around a table. Each boy says that his neighbours are liars. Prove that at least $7$ out of $20$...
2
votes
1answer
130 views

What is the name of this puzzle?

Anyone knows what is the name of this puzzle:
2
votes
2answers
392 views

Winning a restricted game of Nim?

Given the following piles, find the Grundy number of the initial position and make the first move in a winning strategy given that no more than two sticks may be removed from a pile at any time. Pile ...
3
votes
2answers
483 views

find maximum area

Consider a problem here : There is a wall in your backyard. It is so long that you can’t see its endpoints. You want to build a fence of length L such that the area enclosed between the wall and the ...
4
votes
1answer
157 views

General approach to puzzles such as the “$6$ books puzzle”

Six different books $(A,B,C,D,E,F)$ of identical size are stacked as in the figure. We know $A$ and $D$ are not touching. $E$ is between two books which are both vertical or both horizontal. $C$ ...
0
votes
1answer
788 views

Riddle: Minimum time to cross the bridge?

I've recently been asked to solve a riddle, which sounds something like that: There are 4 people on the one side of the bridge. They have only 1 flashlight. It takes respectively 1, 2, 5 and 10 ...
0
votes
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
411k 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
568 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
347 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
185 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
75 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
103 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
75 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
219 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
357 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
76 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
331 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
252 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
424 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
550 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…

...
2
votes
3answers
122 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
362 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 ...