- The 21 pieces are placed down on a desk or the floor with the "Math Fun" piece showing and visible the whole game, like above.
- Players take turns picking up at least 1, and up to 3 pieces at a time.
- Whoever must pick up the Math Fun piece loses.
I prompt them with questions like "Well, what worked?" The winner will definitely have figured out what to do at the end, but they won't need to step it all the way back to the start to win games, so they don't. Then we start discussion around the question "Well, in what situation are you sure to win?" We decide to not count the Math Fun piece because it's pretty much irrelevant and we go through each situation that occurs at the end of a player's turn assuming their opponent is playing perfectly. It's fun for them think their way through it, and my students have been able to figure out the situations below with minimal prompting.
1- You lose, opponent takes 1.
2- You lose, opponent takes 2.
3- You lose, opponent takes 3
4- You WIN, opponent has to leave you with 1, 2 or 3.
5- You lose, opponent takes 1, leaving you with 4.
At #8, they might see the pattern, at 12 they are sure of it.
"So, could we.... write a linear equation that would tell us the winning numbers?"
"If we counted the Math Fun piece, how would our winning situations change? How would the equation change?"
blahblahblah Slope, blahblahblah y-intercept. Hooray for math!
Which player has the advantage if both play perfectly?
What if you could take up to 4 pieces? Only 2? 10?
What if you split it into 2 piles, with two special pieces, and could only take from one at a time?