Crack the Code
How it works
Crack the Code is a 2 player game. Here's how to play:
One player is the codemaker and the other player is the codebreaker.
The codemaker makes a secret code using Xs and Os. The code must have 3 symbols (for example, XOX, OXX, OOO, etc.).
The codebreaker gets 4 guesses to guess the secret code. After each guess, the codemaker tells the codebreaker how many places their guess matches the secret code (but not which places).
The codebreaker wins if they guess the secret code before they run out of guesses. If they run out of guesses before they guess the secret code, the codemaker wins.
Can the codebreaker guarantee that they win every time, no matter what the secret code is? What if the secret code has 4 Xs and Os instead of 3? How many guesses would the codebreaker need? What if the code can include dashes (–) instead of just Xs and Os?
In this activity, students work together to figure out how to beat a facilitator if the facilitator is the codemaker and the students are the codebreakers. If students are able to find a strategy they can use to guarantee they can win against the facilitator, they explore variations of the game and try to come up with expert strategies for these variations as well.
Why we like this activity
It’s fun! Students enjoy playing the game and trying to beat the facilitator.
It helps students to develop logical reasoning.
It helps students to develop algorithmic reasoning.
It requires students to engage in mathematical habits of mind:
- Using logic and finding and using strategies to win as the codebreaker
It has a low floor and a high ceiling: Students can start playing the game by trial and error, but using logic to try to be certain about what the code is and finding a strategy that guarantees that you can crack the code every time is more challenging.
This activity was developed in collaboration with the Julia Robinson Mathematics Festival.