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- New webpage at www.vadimkulikov.org March 24, 2017
- (Ir)rational Behavior of Calculation October 18, 2011
- The Product of Topological Spaces Does Not Obey Cancellation October 12, 2011
- Wild Embeddings October 11, 2011
- Progress October 4, 2011
- Class-metric August 24, 2011
- Intellectual Lazyness August 22, 2011
- Time Limit: One Minute! August 17, 2011
- Douglas Hofstadter: I Am a Strange Loop. August 15, 2011
- 0.999999……=1? (continuation) July 10, 2011
- Walks on Planets July 5, 2011
- 0.999999….. = 1? July 3, 2011
- Prisoners’ problem 6 June 29, 2011
- I am back! June 28, 2011
- A non-associative “group” March 21, 2011
- Why I haven’t blogged March 21, 2011
- Doodling with Fractals and Persistent Worms. January 2, 2011
- Five groups November 23, 2010
- Splitting A Rectangle November 17, 2010
- Sphere November 10, 2010
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Category Archives: Recreation
Time Limit: One Minute!
I found this lovely geometrical riddle in Martin Gardner’s book “My Best Mathematical and Logic Puzzles”. The most lovely thing about it is that Gardner gives a time limit: one minute! So, now draw out your stopwatch and read the … Continue reading
Posted in Geometry, Mathematics, Popular, Recreation, Wednesday Problem
11 Comments
Walks on Planets
My gps-equipped radiowave controllable robot Lori is somewhere on the surface of Earth. I order her to drive 100 miles South and she obeys. Then I order her to drive 100 miles West and she obeys. Then I order her … Continue reading
Posted in Geometry, Mathematics, Popular, Recreation, Wednesday Problem
7 Comments
Prisoners’ problem 6
Three prisoners meet a guard. The guard says: I have hats with me, two of which are black and the others are white. The prisoners ask: “How many hats there are all together?” He says: “It’s a secret!”. The guard … Continue reading
Doodling with Fractals and Persistent Worms.
Suppose we have a rubber line of length 1 m and a worm at the other end. The worm moves 10 cm in a minute and its goal is to reach the other end moving along the rubber line. However … Continue reading
Posted in Combinatorics, Geometry, Mathematics, Recreation
1 Comment
Splitting A Rectangle
Find all ways to cut a rectangle into two connected pieces of equal area so that they can be rearranged to get a new rectangle with different dimensions (side lengths) than the orgininal one. I already know countably many ways. … Continue reading
Posted in Geometry, Mathematics, Recreation, Wednesday Problem
2 Comments
A Year Problem
There are more year problems than years. But since I have been pondering on this particular one, I will present it here. You are allowed to use +, -, / and * (plus, minus, division and multiplication) signs and bracketing. … Continue reading
Posted in Algebra, Combinatorics, Mathematics, Recreation, Wednesday Problem
12 Comments
More Chessboard
You are free to comment your solutions, questions and remarks.. You have two kinds of allowed moves. One move is to jump with a piece over another piece in a horizontal or vertical direction like this: and to jump with … Continue reading
Posted in Combinatorics, Games, Mathematics, Recreation, Wednesday Problem
Tagged chess board
3 Comments
Prisoners’ Problem 5
There is a famous class of problems concerning public announcements. There is a philosophical (sociological) appeal in these problems. Can a public announcement change the behaviour of the citizens? Of course, if it is for example a news article about … Continue reading
Posted in Combinatorics, Mathematics, Philosophy, Recreation
Tagged Prisoners' problems
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Incomplete Chess Board
Please comment your solutions, questions and remarks.. I learned this puzzle from Juha Oikkonen, but it is probably quite famous anyway. You have left your chess board on the table in the summer house and when you came back you … Continue reading
Posted in Combinatorics, Games, Mathematics, Recreation, Wednesday Problem
Tagged chess board
2 Comments
Poisoned Bunnies
Please comment your solutions, questions and remarks.. Imagine that you have one thousand bottles in front of you. You know that one of them is filled with poison and others with water, but you do not know which one is … Continue reading
Posted in Combinatorics, Mathematics, Recreation, Wednesday Problem
7 Comments
Euler’s Riddle
Please comment your solutions, questions and remarks.. I found in a recreational book the following riddle attributed to Leonard Euler. The book gives a clumsy solution involving solutions of quadratic equations, a lot of fractions and half a page of … Continue reading
Posted in Algebra, Mathematics, Recreation, Wednesday Problem
2 Comments
How To Find Your Way Out of Woods
Please comment your solutions, questions and remarks.. A lumberjack got lost in a forest. He knows that the area of the forest is S and that there are no meadows in the forest. Show that he can get out from … Continue reading
Posted in Geometry, Mathematics, Recreation, Wednesday Problem
3 Comments
Prisoners’ problem 4
The rules are as in the previous problem, but this time there are only 100 prisoners. How should they do so that 50 of them certainly survives? 3/5
Posted in Combinatorics, Mathematics, Recreation, Wednesday Problem
Tagged Prisoners' problems
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Prisoner’s problem 3
Please comment your solutions, questions and remarks.. There are infinitely many prisoners in a prison. The prisoners are taken to the yard and everyone is given a hat which is either black or white. No one knows the colour of … Continue reading
Posted in Combinatorics, Mathematics, Recreation, Set Theory, Wednesday Problem
Tagged Prisoners' problems
2 Comments
Prisoner’s problem 2
Please comment your solutions, questions and remarks.. Consider a prison with several millions prisoners. The head of the prison arranges the following challenge to the prisoners. One prisoner at a time will be called to a room with a lamp. … Continue reading
Posted in Mathematics, Probability, Recreation, Wednesday Problem
Tagged Prisoners' problems
2 Comments
Prisoner’s problem 1
Please comment your solutions, questions and remarks.. We are going to have several prisoner problems! Better solve them before you end up in jail. There are 2010 prisoners in the prison. One day the chair of the prison gathers the … Continue reading
Posted in Combinatorics, Mathematics, Recreation, Wednesday Problem
Tagged Prisoners' problems
5 Comments
Andre’s Reflection Method
I promised to post something about random walks. I learned the content of this post while listening to Vilppu Tarvainen’s bachelor’s degree talk and I consider it is quite cute. Let us consider a one dimensional random walk: formally it … Continue reading
Posted in Combinatorics, Mathematics, Probability, Recreation
1 Comment
How Many Are True?
Please comment your solutions, questions and remarks.. At most 1 statement of this post is true. At most 2 statements of this post are true. At most 3 statements of this post are true. At most 4 statements of this … Continue reading
Posted in Logic, Mathematics, Recreation, Wednesday Problem
1 Comment
Sorry I Am Late
Please comment your solutions, questions and remarks.. How many of the statements below the line are true? 2/5 ———— This post was not published on Wednesday 24. February 2010 There are at least 2 true statements in this post (after … Continue reading
Posted in Logic, Recreation, Wednesday Problem
3 Comments
Pinocchio Is Omnipotent
Please visit my new website at www.vadimkulikov.org to find more about mathematics, science, cognitive science and art!
Posted in Logic, Mathematics, Philosophy, Recreation
15 Comments
More Tricks With Triangulations
Please comment your solutions, questions and remarks.. I learned this riddle from Sergei Chmutov. It is also a problem concerning triangulation and sharp angled triangles. Suppose we have a triangulated regular polygon with odd number of edges. The vertices of … Continue reading
Posted in Geometry, Mathematics, Recreation, Wednesday Problem
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Stable Marriages
Suppose n men and n women survived after a spaceship crush on a planet orbiting Alpha Centauri. They happen all to be heterosexuals and all single (or their partners died in the crush). Each man then ranks women in order … Continue reading
Posted in Combinatorics, Mathematics, Recreation
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Triangulation
Please comment your solutions, questions and remarks.. In the last week’s many in one post I explained what is a triangulation. Can you triangulate a square using only sharp angled triangles (i.e. triangles whose all angles are <[tex]\pi/2[/tex])? For example … Continue reading
Posted in Geometry, Mathematics, Recreation, Wednesday Problem
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The Coin Placing Game.
See the Wednesday Problem’s vague rules here. Some games again. According to Sam, from whom I heard this riddle, it divides people into cathegories i) those who realize the answer immidiately and ii) those who think quite long about it. … Continue reading
Posted in Games, Recreation, Wednesday Problem
6 Comments
How Old Are The Kids?
Please comment your solutions, questions and remarks.. This is quite famous. But maybe you haven’t heard it yet: A math student goes to a party organized by her supervisor. The student asks: How many daughters do you have? And the … Continue reading
Posted in Combinatorics, Recreation, Wednesday Problem
2 Comments
The Monk
Please comment your solutions, questions and remarks.. The posts have been a bit advanced lately. Let us lighten the atmosphere by this riddle which admits a simple solution, though mathematicians tend to use calculus in solving it: An Indian monk … Continue reading
Posted in Calculus, Recreation, Wednesday Problem
2 Comments
Joulupukki Is Fair: Your Christmas Riddle
Please comment your solutions, questions and remarks.. Joulupukki came to a kindergarten. He had some number of candies to give to the children. He saw that there are more boys than girls and that he could divide the candies evenly … Continue reading
Posted in Mathematics, Recreation, Wednesday Problem
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The Game Discrete
Inspired by my post about tic-tac-toe I want to introduce a game. It is played on a 3x3x3 grid or equivalently on a 9×3 grid:
Posted in Combinatorics, Games, Mathematics, Recreation
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Handshaking Lemma
Please comment your solutions, questions and remarks.. This one I learned from Sam Hardwick. Show that the number of those, who have shaken their hands with others an odd number of times, is even. Level 1/5 P.S. This lemma has … Continue reading
Posted in Combinatorics, Recreation, Wednesday Problem
2 Comments
Ants
Please comment your solutions, questions and remarks.. This funny riddle I heard from Marcin Sabok. There are n ants on the unit interval, [0,1]. Each has a direction, left or right. In the picture above there are three ants and … Continue reading
Posted in Mathematics, Recreation, Wednesday Problem
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The Chocolate Game
Please comment your solutions, questions and remarks.. I heard this from Lauri Hella, but he doesn’t remember from whom he heard this. The game is played between two players as follows. There is an [tex]n\times m[/tex] bar of chocolate on … Continue reading
Posted in Combinatorics, Games, Mathematics, Recreation, Wednesday Problem
2 Comments
Tic-tac-toe And A Non-Constructive Proof
Usually the game tic-tac-toe is played on an infinite board (i.e. 30 times 40 or something). The two players draw X:s and 0:s to the squares of a notepad paper. Player 1 (beginner) is the X-drawer and the Player 2 … Continue reading
Posted in Combinatorics, Games, Mathematics, Ramsey Theory, Recreation
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Erdös and the individual property of dimensions 1 and 2.
Some time ago I read a biography of Paul Erdös titled ‘my brain is open’ written by Bruce Schechter. The book contains some popular exposition of math. As a biography the book is good, but much of the mathematics and … Continue reading
Posted in Geometry, Mathematics, Recreation
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A liar’s paradox
I will hereby argue that I am the Pope. Consider the following sentence: If this sentence is true, then I am the Pope. It is an implication, i.e. a sentence of the form [tex](A\to B)[/tex], where A is “this sentence … Continue reading
Posted in Philosophy, Recreation
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