# Numerical Tic Tac Toe

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I was super excited to discover a mathematical variation of tic-tac-toe.

Instead of playing with Xs and Os, Numerical Tic Tac Toe is a game of evens vs odds.

I printed the even and odd numbers on different colors of paper to make it super clear which numbers belong to each person.

You might have noticed that the odds have one more number than the evens. As a result, whichever player has the odds ALWAYS GOES FIRST.

On your turn, place one of your numbers on the tic-tac-toe board. Remember – odds always goes first. Each number can only be used once. The winner is the first player to complete a line (horizontal, vertical, or diagonal) with a sum of 15. The line may contain both even and odd numbers.

Numerical Tic-Tac-Toe was invented by Ronald Graham.

My students really enjoyed playing tic-tac-toe, so I think they will enjoy this variation. There’s a bit more logic and strategy involved than traditional tic-tac-toe.

I love putting activities like this up on my dry erase board for students to tackle on their own when they have extra time before class starts or after they finish their assignment for the day. I never make a big deal of the puzzle/game on the board.

I don’t even usually announce that it is there. I just post it on the board and see what students do with it.

I also created a desktop version if you would prefer to have students play at their desks.

After I shared this to Twitter, I learned that Paul Jorgens calls it 15 Tic Tac Toe. He recommends adding the number 0 as well!

Michael Pershan recommends checking out another version of tic tac toe from Beast Academy called Integer Tic Tac Toe. Very interesting! The goal in this game is to get a row with a sum of 0.

Want even more tic tac toe goodness? Check out this journal article about numerical tic tac toe that has information on another variant of the game!

## Digital Version of Numerical Tic Tac Toe

Kathy Henderson has created a digital version of this numerical tic tac toe game in Desmos Activity Builder that you might be interested in.