Math concepts: subtraction within 100, number patterns, mental math
Number of players: 2 or 3
Equipment: printed hundred chart (also called a hundred board), and highlighter or translucent disks to mark numbers — or use this online hundred chart
Set up
Place the hundred chart and highlighter where all players can reach them.
How to play
- Allow the youngest player choice of moving first or second; in future games, allow the loser of the last game to choose.
- The first player chooses a number from 1 to 100 and marks that square on the hundred chart.
- The second player chooses and marks any other number.
- On each succeeding turn, the player subtracts any two marked numbers to find and mark a difference that has not yet been taken.
- Play alternates until no more numbers can be marked.
Endgame
The player who marks the last number wins the game.
For advanced students
When you play Euclid’s game on paper, circle the original pair of numbers. Collect several finished game boards. Compare the pattern of the numbers marked on each game.
- Can you explain why some games have few numbers marked and others have many?
- If you knew the first two numbers, would you be able to predict how many squares would be marked in the end?
For a hint, check out this page at Amby’s Math:
Comments
I first discovered Euclid’s game at Alexander Bogomolny’s outstanding website, Cut the Knot. You can play a Java version online here:
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This is post #3 in my Hundred board series.
Have more fun on Let’s play math! blog:




4 responses so far ↓
Andrée // January 27, 2008 at 9:23 pm
Excellent! Don’t know why I didn’t think of this streamlining of the paper-pencil game. thank you.
Denise // January 28, 2008 at 9:31 am
I’m glad you liked it. Playing with pencil on scratch paper is quick and easy, but using the hundred chart as a game board makes it feel more like a “real” game to me — and the number patterns show up clearly on a chart.
Magic and Mayhem » Blog Archive » A little math game // February 2, 2008 at 1:24 pm
[...] discovered a list of great math blogs today and on one of them I found this little math game. I’m going to print some out and try it with the kids. I don’t think it will work [...]
Carnival of Mathematics 1000 « JD2718 // February 22, 2008 at 5:59 pm
[...] Daniel discusses starts with a comparison of a physical and a mental game. 12 - There is a nice little game with lots of subtraction practice at Let’s Play Math. 12 - A well-chosen diagram can blow the lid off an elementary problem. [...]
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