In tic-tac-toe, 2 players take turns writing Xs and Os on a grid, each hoping to line up 3 in a row. Well, try tic-tac-toe times 10: You make a giant tic-tac-toe board like this, where EACH square is its own little tic-tac-toe board! Each time a player wins a board, that whole square now counts as that player’s shape (X or O), and whoever gets 3 giant squares in a row wins. How do you play? When a player fills in any little square, the next player has to go to the mini-board in the matching part of the giant board. So if someone fills in the top left square of any board, the other player must go now to the top left board. As the boards fill up, you have to avoid sending the other player to a board where he or she could win. Then you could make a board with 9 of these boards on it…and play even longer!
Wee ones: How many spaces does a regular tic-tac-toe board have? See if you can count them all!
Little kids: If 5 squares are filled in with Xs on a regular tic-tac-toe board and the rest are filled with Os, how many Os are there? Bonus: If you fill in the top left corner of the board, in how many directions could you win 3 in a row?
Big kids: In this giant board with a mini tic-tac-toe board in each square, how many tiny squares are on the whole page? Bonus: If you can fill in any square on the center board, and then that player can fill in any square on the next board, how many possible pairs of first 2 moves can the game have?
Wee ones: 9 spaces.
Little kids: 4 Os. Bonus: In 3 directions: across, down, or on the diagonal to the bottom right.
Big kids: 81, since it’s 9 x 9. Bonus: 80 pairs. Each of the 9 squares leads to 9 possible choices on the next board which would be 9 x 9 = 81…but if you fill the center square on that center board, now there are only 8 squares open on that board, not 9.
Laura Bilodeau Overdeck is founder and president of Bedtime Math Foundation. Her goal is to make math as playful for kids as it was for her when she was a child. Her mom had Laura baking before she could walk, and her dad had her using power tools at a very unsafe age, measuring lengths, widths and angles in the process. Armed with this early love of numbers, Laura went on to get a BA in astrophysics from Princeton University, and an MBA from the Wharton School of Business; she continues to star-gaze today. Laura’s other interests include her three lively children, chocolate, extreme vehicles, and Lego Mindstorms.