A surprising solution to the (in)famous "Cross the Network" puzzle

My father introduced me to the "Cross the Network" puzzle when I was a kid. Here it is, as described by Martin Gardner in one of his early Mathematical Recreations columns, which ran in Scientific American from the 1930s to the 1980s.

One of the oldest of topological puzzles, familiar to many a schoolboy, consists of drawing a continuous line across the closed network shown in Figure 51 so that the line crosses each of the 16 segments of the network only once. The curved line shown here does not solve the puzzle because it leaves one segment uncrossed. No "trick" solutions are allowed, such as passing the line through a vertex or along one of the segments.

It turns out there is a solution. Is it a "trick?" That's up for you to decide.

This puzzle, and many others, are in Gardner's Hexaflexagons and Other Mathematical Diversions: The First Scientific American Book of Puzzles and Games. Used copies available cheap! Read the rest

My trip through the Starmaze: a world in the 9th dimension

There are times when I get tired of all of the major sites and apps that make up a lot of the seen Internet. Sadly, I was born too late to experience the wonder of Geocities and intricate handmade websites run by just a single person. But, on some evenings, I still search for those smaller websites that no one else normally sees. I find the wonder of coming across hidden blogs and pages really fun.

It was a night like this when I stumbled across John Cartan’s writing about the Starmaze last year, and I quickly became fascinated. Unlike every other corner of the web, Cartan’s website wasn’t trying to sell me a useless product or tell me about news I’ve already heard a dozen times. It was instead a series of journal-like recordings about some strange discovery that he called the Starmaze. 

It started with a game he had come across on a computer years ago that involved a square divided into nine sections where each section could be turned on or off. The game began with the middle section of the grid turned on, and the outer eight sections turned off. Clicking one of the sections would turn on/off other parts of the grid in a predictable way, but you could only click the sections that were already turned on. The goal was to click the sections in a way to end up with the outer eight squares turned on, and the innermost square turned off.

Being interested in games myself, this sounded familiar to me immediately. Read the rest

Can you solve the "scrambled box tops" puzzle?

Here's a puzzle from Martin Gardner's Mathematical Games column, which ran for many years in Scientific American. I found it in his low-priced Dover edition anthology, My Best Mathematical and Logic Puzzles.

Imagine that you have three boxes, one containing two black marbles, one containing two white marbles, and the third, one black marble and one white marble. The boxes were labeled for their contents – BB, BW, WW – but someone switched the labels so that every box is now incorrectly labeled. You are allowed to take one marble at a time out of any box, without looking inside, and by this process of sampling you are to determine the contents of all three boxes. What is the smallest number of drawings needed to do this?

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Watching this guy solve a sudoku is deeply satisfying

Simon Anthony is cohost of a sudoku YouTube channel called Cracking the Cryptic. In this video he solves a difficult sudoku puzzle with extra constraints. It's really fun to watch him solve it and get more excited as his sense of wonder grows ("This is like the universe is singing to us," he says as he begins to realize that it is solvable). I watching the whole 25-minute video.

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Can you rearrange these cards, sudoku style?

Here's a fun puzzle with an easy setup that makes for a good stay-at-home time-filler. Like sudoku, see if you can rearrange these cards so that no face or suit repeats itself in any column, row, or diagonal. Watch the video if you need some help. Read the rest

Watch a master solve a nightmare ring puzzle

An old man in Japan owns a vintage topological puzzle, a little monster so difficult to solve that it ended up on Knight Scoop being taken to a physics professor, a professional magician and a chimpanzee in an effort to figure it out. Eventually a ring puzzle master shows how it's done (10:40 if you're pressed for time).

UPDATE: This is clearly the same puzzle Rusty blogged back in 2017 in a post that's lost its YouTube. It's now so famous there's a website about the puzzle which sells replicas of it on Amazon. Read the rest

Why this sliding tile puzzle arrangement is impossible

You are probably familiar with these little tile slide puzzles with 15 tiles that slide around in a 4 x 4 grid. The object is to slide the tiles around so that the tiles marked 1 through 15 are arranged in numerical order. The card that comes with the puzzle shows a number of different ways to arrange the numbers, including arranging the tiles in reverse numerical order. In this episode of Numberphile we learned why this particular arrangement is impossible.

: YouTube Read the rest

Chocolate Fix: a favorite puzzle game

The puzzle game Chocolate Fix has been a family favorite around our house for years.

Can you solve the "artist's dilemma" problem?

I found this puzzle in a book I've had since I was a kid:

Simply put, your task is to draw the figure at the right without crossing a line, without taking your pencil from the paper and without retracing a line.

The book is called Merlin's Puzzler. It's out of print, but used copies are pretty cheap. Read the rest

Cool magic trick: The Perpetual Puzzle

Tenyo is a Japanese magic trick company that's been around since 1960. They are well known for making clever props. (My friend Richard Kaufman, who often writes for Boing Boing, wrote a 1,400-page two-volume set about the company, called Tenyoism)

Here's a Tenyo puzzle trick called The Perpetual Puzzle (It's available on Amazon). You start by showing a rectangle made from 5 pieces. The rectangle fits snugly in a black plastic frame. Next, you show a sixth piece and combine it to the other five to make a larger rectangle. This rectangle also fits perfectly inside the frame. Finally, you show an even larger seventh piece, add it to the other six to form a rectangle. It, too, fits into the frame. How is it done? (If you know, please don't reveal the secret in the comments.) Read the rest

Weird and wild warped-grid jigsaw puzzles inspired by Mobius, Haeckel, and Picasso

Mathematician, artist, and engineer George W. Hart of "Möbius strip bagel" fame has recently been playing with a laser cutter to create head-spinning warped-grid jigsaw puzzles. He came up with an algorithm to generate the initial patterns but "the real fun is step 2," he says, "using a geometric transformation to warp things."

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Unknown Pleasures puzzle

Portland Laser Co. offers a puzzle based on Joy Division's famous cover to Unknown Pleasures, a plot of signals emitted by pulsar CP 1919. Yours for $50.

One of the most iconic album covers of all time, made into a puzzle.

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Can you solve the "Hanging Cable" problem, used as an Amazon interview question?

A cable of 80 meters is hanging from the top of two poles that are both 50 meters off the ground. What is the distance between the two poles (to one decimal point) if the center cable is (a) 20 meters off the ground and (b) 10 meters off the ground?

Presh Talwalker of Mind Your Decisions says the above riddle was used as an Amazon interview question. His video has the answer.

Image: YouTube Read the rest

How many triangles do you see?

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A post shared by Popular Mechanics Magazine (@popularmechanics) on Jan 29, 2020 at 12:14pm PST

Sure, you can count them. I did, and, er, I missed a few. Or you can take one of the approaches suggested by the mathematics professors that Andrew Daniels interviewed in Popular Mechanics:

“I would approach this just like one approaches any mathematical problem: reduce it and find structure,” says Sylvester Eriksson-Bique, Ph.D., a postdoctoral fellow with the University of California Los Angeles’s math department.

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Chess: take the Knight's tour online

The Knight's tour is a traditional chess problem where a lone knight is placed on a chess board and must visit each square only once. You can play this perfectly simple free implementation created by u/psrwo on Reddit. The source code is at github. The knight is randomly placed at the outset.

I can't visit more than fifty-something squares, because I'm terrible at stuff like this. Read the rest

Highlights from the Red Bull Rubik’s Cube World Cup

The Red Bull Rubik’s Cube World Cup was held November 17 in Moscow. Competitors squared off in four events:

3x3 Speed Cubing - solving the Rubik’s Cube as fast as possible; Fastest Hand - a challenge that solves the Rubik’s Cube with only one hand; Re-Scramble - pits competitors trying to replicate a computer generated pattern from another cube as fast as possible and; 3x3 Female - a track exclusively for female competitors.

Here are highlights from the event, which was attended by Erno Rubik himself:

Red Bull has also posted a series of instructional videos on solving Rubik's Cubes:

Read the rest

Where is the 5th pig?

This is an anti-fascist puzzle made in occupied Netherlands circa 1940. Can you find the 5th pig? (Hint: Al Jaffee would have no problem finding it.)


[via r/interestingasfuck] Read the rest

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