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 ...
2
votes
0answers
88 views
Can 24 lines on a cubic surface be realized as 24 identical spiral rods?
It's possible to put 24 lines on a cubic surface. 27 lines is possible, but I don't have a great picture for that surface. It turns out that the 24 lines can be built with Zome. I'm thinking that ...
0
votes
4answers
286 views
Can you help me solve these questions related to a Logical theory?
In a group of 200 people, number of people having at least primary education (assuming - Category I): number of people having at least middle school education (Category II): number of people having ...
5
votes
1answer
118 views
A small geometry puzzle out of curiosity
Out of curiosity I've been thinking about the following "puzzle" for a while now and maybe someone here can help.
Situation
We take a rectangle and start off at one of the corners. In that corner, ...
2
votes
2answers
126 views
Divide $40$ to $4$ parts such that every number from $1-40$ can be realized
How can you divide $40$ to $4$ parts such that every number from $1-40$ can be realized just by adding or subtracting those $4$ parts?
7
votes
2answers
413 views
Find missing number from sum of first few natural numbers
A child was asked to add the first few natural numbers $1+2+3+...$ as long as his patience permitted. As he stopped, he gave the sum as $575$. When the teacher declared the result wrong, the child ...
4
votes
3answers
136 views
What is the value of D here?
Number S is obtained by squaring the sum of digits of a two digit number D. If the difference between S and D is 27, then the two digit number D is?
My thoughts:
Let the two digit number $D$ be ...
1
vote
1answer
66 views
Explanation for a peculiar property of a number
I had come across a problem, where 2 people play a game where think of a number n, and turn by turn subtract a number $p$ from $n$ where $p$ is a prime and is $p < n$ and 1 is taken as prime here. ...
0
votes
1answer
42 views
Find out the length of a recurrence
I have this rules for creating a list of numbers:
$x/2$ if $x$ is even, repeat
$3x+1$ if $x$ is odd, repeat
if $x=1$, stop
so for example, starting from 15, the list will be: 15, 46, 23, 70, 45, ...
0
votes
4answers
131 views
A logic puzzle from TES: Arena
Its nice when games have riddles hidden in them. While playing TES:Arena, I came across an unusual logical puzzle:
There are 3 cells.
If Cell 3 holds worthless brass, Cell 2 holds the gold key.
If ...
2
votes
2answers
134 views
What area of mathematics is this problem asking about? [closed]
A colleague posted this on a whiteboard (as a brain-teaser I guess):
A $\rightarrow$ B;
B $\rightarrow$ C;
AD $\rightarrow$ E;
BE $\rightarrow$ C;
BF $\rightarrow$ D;
AC $\rightarrow$ F
What is ...
4
votes
3answers
148 views
How to formally model the “hesitation” in the hat-guessing puzzle?
Hua Luogeng (in Chinese, 华罗庚) took a hat-guessing puzzle as an illustration in a booklet focusing on mathematical induction. The following description is a literal translation from Chinese.
...
17
votes
1answer
1k views
The $n$ Immortals problem.
I saw this riddle posted on reddit a long time ago, called the "Seven Immortals."
In the beginning, the world is inhabited by seven immortals, ageless and sexless, who begin to multiply and ...
6
votes
4answers
229 views
A math teacher thought of a positive integer of two digits.
A math teacher thought of a positive integer of two
digits. She wants her two intelligent students Hanna
and Charlie determine the exact number thought.
For this, Hanna is privately told how many ...
-1
votes
1answer
317 views
If 2 x 6 = 4, 4 x 1 = 7 and 8 x 3 = 1 find the value of 5 x 5.
Please help me find some logical pattern for
If 2 x 6 = 4,
4 x 1 = 7
and 8 x 3 = 1
find the value of 5 x 5.
2
votes
1answer
100 views
Monty Hall Application
Driver A comes to a 3 way path junction but is not sure which one to take.
Just as he decides to take path 1, a cyclist came by and told driver A all he knows is that he is going on path 3 which would ...
1
vote
1answer
70 views
What are good methods for solving Conway's card-stacking puzzle?
Suppose there is a table with three marked spots, $A, B, $ and $C$, on which playing cards can be put, face up. Initially, an ace (1), a deuce (2), and a trey (3) are placed on one or more of these ...
0
votes
0answers
113 views
Room switching logic puzzle
How can one solve this logic puzzle?
I think the key ideas may have something to do with 11.,12. and common knowledge
An Arab man and an Israeli woman are abducted by extraterrestrials. The E.T.s ...
1
vote
1answer
219 views
Puzzle on the triangle.
In triangle top four figures that have to be repositioned to form the "triangle" without a unit square.
How to explain this?
Thank's.
0
votes
4answers
107 views
Is there a theorem that disproves this or is this just some made up meaningless thing?
I find this slightly funny. I saw this on a meme:$$\begin{align}a=x\\ a+a=a+x\\ 2a=a+x\\ 2a-2x=a+x-2x\\ 2(a-x)=a+x-2x\\ 2(a-x)=a-x\\ 2=1\end{align}$$ How can these strange algebraic manipulations not ...
-11
votes
1answer
2k views
What is the logical pattern in these pictures? [closed]
What is the pattern/logic in these two (separate) logical/pattern recognition tasks? I could not find it, it may be hard.
Which symbols should replace the question marks?
Edit:
What is the logic ...
10
votes
1answer
242 views
Given a set of digits, what is the biggest number we can make using exponentiation - numberphile noodle quiz
The question is motivated by a question on a can of number noodles.
Each item is a digit between $0$ and $9$. Clearly, if you form a string and consider it to represent a base $10$ integer, then ...
-1
votes
1answer
290 views
knight and knave problem
For this question, suppose you are on the island of knights and knaves. Remember that knights always speak truth while knaves always tell a lie.
(a) Suppose you come across two of the natives. You ask ...
2
votes
2answers
170 views
Use three 11's and various math symbols to make an equation equal to 6
The puzzle is to use the following symbols $$+,\;-,\;*,\;/,\;(\;,\;),\;!, \;\sqrt(\cdot)$$ in order to make a valid equation out of $$11~~~~~~11~~~~~~~11 = 6.$$
(There are three elevens with space in ...
2
votes
2answers
60 views
Tower of dice - Abstracting a practical problem to a mathematical method
This question arose when playing yahtzee with some friends. Not entirely sure if I'm in the right area, but hope you can help.
How many dice do you need to create a tower whose walls have the same ...
3
votes
0answers
57 views
Card passing game, maximum length
Quoting from this question:
There are 25 people sitting around a table and each person has two cards. One of the numbers 1,2,..., 25 is written on each card, and each number occurs on exactly two ...
3
votes
2answers
150 views
A less challenging trivia problem
There are 25 people sitting around a table and each person has two cards. One of the numbers 1,2,..., 25 is written on each card, and each number occurs on exactly two cards. At a signal, each person ...
4
votes
2answers
157 views
Cut the rope puzzle
This question was asked to me in an interview, I still cannot think of its solution. Can anyone help? Following is the question:
Given an infinite number of ropes of length $R$, you have to ...
2
votes
2answers
132 views
Prove or disprove a chessboard with diagonal corners removed, cannot be tiled with L shape pieces or size 2
I think this is impossible, but I don't know how to prove an integer solution doesn't exist for a given equation. Here's my approach:
First, observations:
The removed tile will be of the same color. ...
8
votes
3answers
170 views
Group of sphere transformations, impressing friends
Ok, so here's the story: I am reading a book on algebra and, via some exercises, discovered that in any group $G$, the order of $x \cdot y$, written $o(x \cdot y)$, equals $o(y \cdot x)$. Now, this is ...
-3
votes
2answers
132 views
Find the last number in the given sequence
Find the last number in the given sequence
$$\begin{pmatrix}
4& 9& 20\\
8& 5& 14\\
10& 3& ?\end{pmatrix}$$
(It's $3\times3$ matrix)
2
votes
1answer
270 views
Guess my birthday
This is just a funny question that I was elaborating... I know one way to solve (or maybe it's wrong...), but I want know if there is another way to solve this (when we keep adding conditions, there ...
2
votes
1answer
125 views
Four men seated in a boat puzzle
I am looking for an elegant way to solve this rather simple logic puzzle using mathematical logic (statements, conjunctions, disjunctions, implications, tautologies, predicate logic and so on). I am ...
5
votes
1answer
256 views
Find volume of crossed cylinders without calculus.
I found this puzzle here. (It's labeled "crossed cylinders".) Here's the description:
Two cylinders of equal radius are intersected at right angles as shown at left. Find the volume of the ...
5
votes
0answers
308 views
topology puzzle - without cut the rope, separate two rings
hello I wonder whether this puzzle is possible to solve.
if possible, what kind of thing should I learn to solve this?
the problem is make left one to right one without cut the rope
only stretch and ...
21
votes
3answers
904 views
Guaranteed Checkmate with Rooks in High-Dimensional Chess
Given an infinite (in all directions), $n$-dimensional chess board $\mathbb{Z^n}$, and a black king. What is the minimum number of white rooks necessary that can guarantee a checkmate in a finite ...
0
votes
1answer
44 views
homework cheyenne
It is a four-digit number.
Its largest place value is its one place.
The squares of each of its digits are less than nine.
Its thousandths didgit divided by its ones digits is 50%.
The sum of two pf ...
0
votes
1answer
91 views
three girls gave a friend 60 rupees and asked her to buy them a kilo of mangoes from the market. [duplicate]
Possible Duplicate:
Riddle (simple arithmetic problem/illusion)
three girls have a friend 60 rupees and asked her to buy them a kilo of mangoes each from the market. the mangoes cost 55 ...
1
vote
1answer
194 views
Setting A Paper on Mathematical Puzzles
I need to set a paper for High School Students on Mathematical Puzzles which make the use of logic, simple combinatorics and algebra. Can people provide new and innovative questions.
The questions ...
9
votes
4answers
858 views
Ten soldiers puzzle
This is a puzzle from one popular book called "The Man Who Counted: A Collection of Mathematical Adventures",author is Malba Tahan. How to arrange ten soldiers in five lines in such a way
that each ...
8
votes
2answers
342 views
“8 Dice arranged as a Cube” Face-Sum Equals 14 Problem
I found this here:
Sum Problem
Given eight dice. Build a $2\times 2\times2$ cube, so that the sum of the points on each side is the same.
$\hskip2.7in$
Here is one of 20 736 ...
7
votes
2answers
1k views
Father and daughter river crossing puzzle.
There are 3 men and 3 girls. lets name them ABC, A's daughter X, B's Daughter Y, C's daughter Z.
Rule to cross the river:
At once Only two Can go on boat.
Only Men know how to drive the boat (So ...
2
votes
1answer
90 views
Books in the Library of Babel
I recently came upon a comment in the mathematics overflow stating that the infinite string of pi was similar to The Library of Babel. This library is a universe containing every possible combination ...
2
votes
2answers
72 views
Puzzle on Ranks
Here is a puzzle from textbook : 40 Puzzles and Problems in Probability and Mathematical Statistics
Peter draws n = 100 independent realizations of a continuous rv and ranks them in increasing order ...
4
votes
1answer
142 views
What function does this infinite series represent?
$$\frac14+\frac{x-4}{2!x^2}-\frac{(x-4)(2x-4)(3x-4)}{4!x^4}+\frac{(x-4)(2x-4)(3x-4)(4x-4)(5x-4)}{6!x^6}\mp\ldots$$
Can anyone deduce the sum of this series? The reason I ask is because I made it and ...
1
vote
1answer
88 views
Winning single-pile, variable limits Nim [duplicate]
Possible Duplicate:
Winning strategy for a matchstick game
The rules of this variant of Nim are as follows:
Starting at zero, each player counts up between 1-N numbers. The person that ...
-1
votes
2answers
155 views
Clock Synchronization
There is a clock at the bottom of the hill and a clock at the top of the hill. The clock at the bottom of the hill works fine but the clock at the top doesn't. How will you synchronize the two clocks. ...
9
votes
3answers
554 views
How Strong is an Egg?
You have two identical eggs. Standing in front of a 100 floor building, you wonder what is the maximum number of floors from which the egg can be dropped without breaking it. What is the minimum ...
1
vote
1answer
372 views
How Old Are Children?
Two old friends, Jack and Bill, meet after a long time.
Jack: Hey, how are you man?
Bill: Not bad, got married and I have three kids now.
Jack: That’s awesome. How old are they?
Bill: The product of ...
1
vote
2answers
146 views
A coin-weighing puzzle with 80 coins
In 80 coins one coin is counterfeit. What is minimum number of weighings to find out counterfeit coin?
PS: The counterfeit coin can be heavy or lighter.
2
votes
2answers
120 views
Number of songs sung.
There were 750 people when the first song was sung. After each song, 50 people are leaving the hall. How many songs are sung to make them zero?
The answer is 16, I am unable to understand it. I am ...
