By Geeks out of the Box Posted on

More Math games on a sheet of paper or on the street, using two pieces of chalk

Here come a few simple but beautiful math games that don’t take much time or preparation. Simon has learned about these from the following great resources, worth checking out: Math with Bad Drawings, The 24-Hour Maths Magic Show, Brilliant.org, and, of course, James Tanton on GDayMath.com.

The 9-16 game, source: James Tanton. Each player has to write down the number that is not already on the board but represents the difference between any two numbers that are already on the board. The game starts with placing 9 and 16 on the board. The one who writes the last number possible, wins.
Collector game, source: Math with Bad Drawings. (See the rules written out by Simon in the picture above).
Snake fight, source: Math with Bad Drawings. One player starts in the bottom left, the other player starts in the top right. Each player will grow a snake, one segment at a time. The goal is to cross the other player’s snake as many times as possible. You can’t cross yourself, and you also can’t follow a segment that’s already been drawn (including your own snake, the other player’s or the border). Touching also counts as intersecting. Whoever gets most crosses, wins.
[Don’t remember the name], source: Math with Bad Drawings. In this game, the players place “dominos” on the 6×6 grid. You can claim an area on the grid if you finish a “fence” around it, and it has an odd number of squares below 10. Who claims more squares wins. Source: Math with Bad Drawings
Black Hole, source: Math with Bad Drawings. You have a pyramid consisting of 21 circles. Start placing numbers in the circles (in order, we forgot this in the game below 😅). There will be one circle remaining, which acts as a “black hole” sucking in all the neighboring numbers. Whoever ends up with a bigger sum remaining (aka the least sum getting sucked in by the black hole) wins.
“Magic Square”, source: Math with Bad Drawings. The goal of this game is to get as close as possible to a magic square. Each player secretly writes numbers in the 4 corners. Then the players reveal their numbers to each other, and then each player MUST put the numbers of the other player in the edges. They can be in any order they like. Finally, both players choose a number to put in the middle.
Each player then calculates the sums of their rows, columns and diagonals. A pair of numbers scores 1 point. A trio scores 2 points. A quartet scores 3 points, and so on. Whoever has the most points wins.
The Domino Trick, Source: James Grime in The 24-Hour Maths Magic Show. Start with a complete domino set. Remove all the duplicates. Then, get your volunteer to choose a domino to put aside. Have your volunteer make a domino chain out of the remaining dominos. They will already be mesmerized that it works, but then you show them that the ends of the chain match the domino that they put aside!
Puzzle: Is there another case when the area of a rectangle equals its perimeter? Source: James Tanton
Puzzle: Pick’s theorem says that if you have a grid of points, and draw a polygon upon that grid of points, then the area of the polygon is the number of points on the polygon divided by two plus the number of points inside the polygon minus one. Source: Brilliant.org
Simon’s attempts to prove Pick’s theorem
A hard puzzle, also from James Tanton

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