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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6
votes
1answer
201 views

Puzzle with some sort of math meaning to it?

This picture was posted in the math building at my college! So there has to be some sort of math puzzle/meaning behind it. Here is the picture of the puzzle and the instructions. I have tried this ...
3
votes
0answers
171 views

placing coins on a table with a twist.

consider the classical puzzle, on a circular table, you and a friend take turns placing coins on the table and the first person who cannot do this loses. You can guarantee winning by placing the ...
2
votes
0answers
98 views

Minimum Overlap

You have a set of ten numbers, and you are trying to cover all 4-element subsets of this set. To do this, you choose 5 elements from the set every time and you cover all 4-element subsets of your ...
3
votes
1answer
77 views

Minimal diameter of set of fractions

Let $p_n$ be a pairwise partition of $\{1,2,...,2n\}, n\in \bf N$ where $(a,b)\in p \implies a<b$, and $P_n$ the set of all such pairwise partition. $d(n) := \min_{p_n\in ...
3
votes
2answers
639 views

Riddle that doesn't make sense and makes sense at the same time [closed]

How many letters are there to the CORRECT answer to this question? And if you do get the answer please explain how you got it.
2
votes
7answers
2k views

Measuring water puzzle

Given two unmarked jugs, one which holds 7 liters, and another which holds 11 liters, an unlimited supply of water, and no need to conserve, how do you measure exactly 6 liters? I would also like to ...
1
vote
1answer
730 views

flower pot puzzle

Sara has 6 flower pots, each having a unique flower. Pots are arranged in an arbitrary sequence in a row. Sara rearranges the sequence each day but not two pots should be arranged adjacent to each ...
1
vote
1answer
137 views

Generating a uniformly distributed set of numbers with negatives?

I have a number generator that can generate numbers between 0 and 1. I want to somehow use this generate a set of $N$ numbers that add up to $1$, and include negative numbers. These numbers must be ...
7
votes
2answers
176 views

chameleon puzzle- modified one

In one island there are 3 colors of chameleon 12 blue,15 green and 7 red. When two different color’s chameleon meet together , they convert into third color. What is the number of minimum no. of ...
4
votes
2answers
142 views

why this puzzle works?

Think of a positive integer, call it X. Shuffle the decimal digits of X, call the resulting number Y. Subtract the smaller of X,Y from the larger, call the difference D. D has the following ...
2
votes
1answer
150 views

reducing enemies - geometry puzzle

You are given an irreflexive symmetric (but not necessarily transitive) "enemies" relation on a set of people. In other words, if person A is an enemy of a person B, then B is also an enemy of A. ...
2
votes
2answers
180 views

Puzzle on coins: Designing an operation

A square table has a coin at each corner. Design an execution sequence, each of whose steps consists of one of the following operations: ONE: The operation chooses a coin (possibly a different one ...
3
votes
2answers
209 views

puzzle on parks

A park contains paths that intersect at various places. The intersections all have the properties that they are 3-way intersections and that, with one exception, they are indistinguishable from each ...
2
votes
1answer
545 views

roulette wheel sequence

Is the sequence of numbers around a European roulette wheel (the integers from 0 to 36 inclusive) random or is there a pattern to it? It is said to have been devised by Pascal, which might be thought ...
2
votes
1answer
186 views

Solving the 'insert any number of operators' problem

I recently came across a rather simple problem: express the number 2008 using thirteen zeroes (yes, zeroes). The solution is, obviously, to use the fact that $0!=1$ and consequently attempt to use up ...
5
votes
2answers
519 views

Logic Puzzle of Diamonds and sons

I came across a math problem and I need a solution for this. An old man has 49 diamonds. Each one has a different worth as $1, $2, $3, ….. $49. He has 7 sons and he ...
3
votes
0answers
69 views

Three old chestnuts in elementary geometry: is there a unified perspective? [duplicate]

Coxeter and Greitzer, in their excellent Geometry Revisited, list a few "hardy perennials" in elementary geometry: tough problems solvable by elementary methods. Their problem number 4 (on page 26 in ...
1
vote
1answer
257 views

Logic Puzzle, Two Dollar Bills

I read the following online, and I can't seem to figure it out: A bank robber is planning a heist of a high-tech bank vault. In order to exploit a weakness in the bank's security system, he needs to ...
0
votes
3answers
203 views

Coded language puzzle!! [closed]

Here is a puzzle I can't crack. It goes like this: In a certain coded language MANGO=3/5 ORANGE=2/6 APPLE=1/5 Then, POTATO=?? The answer is 5/6. I would like to know to arrive at the answer.
0
votes
1answer
58 views

Finding possibilities puzzle

The answer: 2 Hi guys, I'm doing the practice papers for an examination, and got stuck on this question. I ended up getting the right answer, but I'm not sure if my thinking is correct. I would ...
4
votes
3answers
767 views

Escalators visible steps question.

A person always walk down on a moving escalator to save his time. He takes 50 steps while he goes down. One day due to power failure of 10 sec, he took 9 seconds more to get down on than his usual ...
5
votes
1answer
397 views

Tricky Puzzle!! Please help.

I stumbled upon a puzzle I can't crack. It goes like this: In a certain Code language: 7321=6 5342=3 8645=15 Then 9312=? The Answer is 9. But I can't seem to find the logic behind it??
1
vote
1answer
172 views

Two ball bounce problem

Two I had an interview, where they have asked me a physics puzzle. The question was, If two balls have been dropped at the same time from same height. suppose ...
4
votes
2answers
2k views

why 64 is equal to 65 here?

how is this possible? I know there is some trick, should someone please explain?!
3
votes
1answer
153 views

Simple tax puzzle

I recently saw some post on facebook whining about taxes. Simplifying it (and changing numbers, facts, etc.), this was saying: For each dollar an employer wants to pay you: 20% go in taxes that ...
2
votes
1answer
127 views

Weird system of equations

X : 2 = 7 Y : 2 = 6 X + Y = 15 Find X and Y. I think maybe this is some unpositional number system. I've tried positional, and it works for basis 21 (if we take X=D, and Y=C), but professor told me ...
5
votes
1answer
213 views

Smullyan-To-Mock-a-Mockingbird, Find egocentric bird in L

Question (29, p. 81). Let me tell you the most surprising thing I know about larks: Suppose we are given that the forest contains a lark $L$ and we are not given any other information. From just ...
4
votes
1answer
179 views

Discounted optimization problem

I have difficulties writing down the following problem in a formal way: We have some coke machines in a school and they can be working or being broken. So we have two states, working and broking. ...
0
votes
1answer
107 views

Exponent Upon Exponent? [duplicate]

I can't understand this. Can you please make a clearer explanation?
5
votes
1answer
198 views

$n$ doors to escape - best strategy

Assume you standing in some place and you have $n$ doors in front of you. When you open one of the doors, lets say the $i$-th door three things can happen. With probability $p_i$ you can escape With ...
19
votes
1answer
926 views

Why are these geometric problems so hard?

I was surprised to learn that both for the Moving Sofa Problem and Packing 11 Squares solutions have been proposed, but in either case the optimality of the proposed solution is, as of yet, only ...
8
votes
4answers
324 views

A statistical approach to the prisoners problem

Two days ago, I found this problem on reddit (I didn't have access to reddit when I did the math, so I did it with 24 instead of 23, and I decided the warden picked someone every day, not "whenever he ...
130
votes
20answers
8k views

Are there any open mathematical puzzles?

Are there any (mathematical) puzzles that are still unresolved? I only mean questions that are accessible to and understandable by the complete layman and which have not been solved, despite serious ...
5
votes
6answers
935 views

Covering a chess board with $2$ missing places with $31$ dominoes

I am reading a book that is intended to a wide audience (and not just mathematicians etc'), the book is, of course, about mathematics (Its still not clear about what exactly, I am only in page $2$). ...
0
votes
2answers
303 views

Help me with this riddle. [duplicate]

We have two variables from 2 to 99. Their sum is A. Their product is B. I know A, the other person knows B. We have to get the numbers without asking each other. But I call the other person and say ...
0
votes
1answer
499 views

Proof by induction in a game with water balloons

Consider the following description of a game. There are $n$ people playing, one of whom leads the game. They are playing on a playing field with no obstacles. Everyone carries one water balloon. ...
2
votes
3answers
814 views

A truth teller and liar puzzle of Ramanujan mathematical olympiad 2013

On an island each person always tells the truth or each person always tells a lie. Three people say $A$ , $B$ and $C$ have a conversation. $A$ says that $B$ is lying , $B$ says that $C$ is lying and ...
5
votes
1answer
284 views

Whats the mathematics behind this type of taking the rope out puzzle.

I know there has to be a way to solve this puzzle with math. I have included a picture, because I don't know the proper terms for this puzzle. I have included two pictures, I believe they are the ...
1
vote
2answers
180 views

Probabilistic puzzle

There are $n+1$ boxes and every box contains $n$ balls. For every $k\in\left\{ 0,1,\ldots,n\right\} $ there is exactly $1$ box containing $k$ white balls and $n-k$ black balls. A box is picked out and ...
8
votes
2answers
192 views

Bit placement puzzle

Consider a binary vector of length $n$ that is initially all zeros. You choose a bit of the vector and set it to $1$. Now a process starts that sets the bit that is the greatest distance from any $1$ ...
3
votes
2answers
2k views

How to create number six using three zeroes?

How to create number 6 using only three 0, any arithmetic operation is allowed? I know it is possible, but I don't know how...
0
votes
1answer
236 views

Filling 4l, 5l bottles from two 10l bottles

There are two bottles of 10litre each filled with water. Now two persons having empty bottles of 4litre and 5litre want to take 2litres of water each from the previous 10litre bottles.. Now you ...
4
votes
1answer
83 views

A persistent difference

Here's a fun math problem. I wasn't able to get it - am curious what you guys have to say. Pick a four-digit number whose digits are not all the same. From its digits form the smallest four-digit ...
8
votes
1answer
222 views

Shop Chocolates puzzle

I was trying to solve a puzzle but was not able to find any solutions if any one knows the solutions please, share. "You own a shop of chocolates. You want to give exact number of chocolates (say ...
-1
votes
3answers
199 views

Is this possible to convert one array to another given array?

you are given two arrays having n elements , like for n=4,suppose array1={1,2,3,4} array2={2,1,4,5} convert array 1 to array2 performing operation minimum number of time . Also state if ...
6
votes
7answers
3k views

answer to iq test with colored squares

What is the best (whatever this means) answer and why?
7
votes
1answer
1k views

Determining the favored penny on a chessboard

Let's suppose there is a chessboard (with 64 squares), and there is a penny on each square. Each of the pennies has a side (head or tails) facing up, chosen at random. I look at the board and choose ...
5
votes
1answer
245 views

Probabilistic riddle

If you choose an answer to this question at random, then what is the chance you will be correct? A) 25% B) 50% C) 60% D) 25% On internet you can find the problem here.
208
votes
41answers
29k views

Riddle: 1 question to know if the number is 1, 2 or 3

I've recently heard a riddle, which looks quite simple, but I can't solve it :/ The girl thinks of a number which is 1, 2, or 3 The boy then asks just 1 question about the number The girl can only ...
0
votes
2answers
215 views

Soda can contest problem

The store's rule is that you can use 3 empty cans to exchange for 1 can of soda. Alex's class has 17 students and each bought a can of soda at the beginning of the party. At most, how many more cans ...