Questions tagged [recreational-mathematics]

Mathematics done just for fun, often disjoint from typical school mathematics curriculum. Also see the [puzzle] and [contest-math] tags.

Recreational mathematics is a general term for mathematical problems studied for the sake of pure intellectual curiosity, or just for the enjoyment of thinking about mathematics, without necessarily having any practical application or expectation of deep theoretical results.

Recreational mathematics problems are often easy to understand even for people without an extensive mathematical education, even if the theory they lead to may turn out to be surprisingly deep. Thus, recreational mathematics can serve to attract the curiosity of non-mathematicians and to inspire them to develop their mathematical skills further.

Many typical recreational mathematics problems fall into the fields of discrete mathematics (combinatorics, elementary number theory, etc.), probability theory and geometry. Important contributors to recreational mathematics are Sam Loyd and Martin Gardner.

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Big List of Fun Math Books

To be on this list the book must satisfy the following conditions: It doesn't require an enormous amount of background material to understand. It must be a fun book, either in recreational math (or something close to) or in philosophy of…
RougeSegwayUser
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"The Bachelorette Problem" (slightly adapted from Tao's Google+ account)

The following puzzle being very much recreational for me, I couldn't resist myself from sharing it with my fellow MSE user friends. Let's have a look at it. You are the most eligible bachelorette in the kingdom, and as such the King has invited you…
user170039
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Any smart ideas on finding the area of this shaded region?

Don't let the simplicity of this diagram fool you. I have been wondering about this for quite some time, but I can't think of an easy/smart way of finding it. Any ideas? For reference, the Area is: $$\bbox[10pt, border:2pt solid…
The Artist
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How to entertain a crowd with mathematics?

I am a high school student who follows a university level curriculum, and recently my teacher asked me to hold a short lecture to a crowd of about 100 people (mostly parents of my classmates and such, I'm not the only one to do something, other kids…
MathisFun
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How does the divisibility graphs work?

I came across this graphic method for checking divisibility by $7$. $\hskip1.5in$ Write down a number $n$. Start at the small white node at the bottom of the graph. For each digit $d$ in $n$, follow $d$ black arrows in a succession, and…
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The Complexity of "The Baby Shark Song".

This question is just for fun. I hope it's received in the same goofy spirit in which I wrote it. I just had the pleasure of reading Knuth's "The Complexity of Songs" and I thought it'd be hilarious if someone could do an analysis of the complexity…
Shaun
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What numbers can be created by $1-x^2$ and $x/2$?

Suppose I have two functions $$f(x)=1-x^2$$ $$g(x)=\frac{x}{2}$$ and the number $1$. If I am allowed to compose these functions as many times as I like and in any order, what numbers can I get to if I must take $1$ as the input? For example, I can…
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Xmas Maths 2015

Simplify the expression below into a seasonal greeting using commonly-used symbols in commonly-used formulas in maths and physics. Colours are purely…
Hypergeometricx
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Can a piece of A4 paper be folded so that it's thick enough to reach the moon?

While procrastinating around the web I stumbled on a page that contained the image below, from cracked.com. I can't help but believe that this is false… Even though the article header says: 22 Statistics That Will Change The Way You See the…
blade19899
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Sharing a pepperoni pizza with your worst enemy

You are about to eat a pepperoni pizza, which is sliced into eight pieces. Each pepperoni will unambiguously belong to some slice (no pepperoni is "between" slices). The caveat is that you have to share the pizza with your worst enemy, and you want…
Mankind
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What are some math books written in dialogue or story form, e.g., a teacher explaining to a student?

Good examples would be The Square Root of 2 by David Flannery or Math Girls by Hiroshi Yuki.
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How many triangles

I saw this question today, it asks how many triangles are in this picture. I don't know how to solve this (without counting directly), though I guess it has something to do with some recurrence. How can count the number of all triangles in the…
Belgi
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Expected number of people to not get shot?

Suppose $n$ gangsters are randomly positioned in a square room such that the positions of any three gangsters do not form an isosceles triangle. At midnight, each gangster shoots the person that is nearest to him. (A person can get shot more than…
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The expected outcome of a random game of chess?

Imagine a game of chess where both players generate a list of legal moves and pick one uniformly at random. Q: What is the expected outcome for white? 1 point for black checkmated, 0.5 for a draw, 0 for white checkmated. So the expected outcome…
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Could the sum of an even number of distinct positive odd numbers be divisible by each of the odd numbers?

Could the sum of an even number of distinct odd numbers be divisible by each of the odd numbers ? Let $k\geq 4$ be an even number. Can one find $k$ distinct positive odd numbers $x_1,\ldots,x_k$ such that each $x_i$ divides $S = \sum_{i=1}^k x_i$…