Cryptic Cards
How it works
You have a deck of cards. One person chooses a secret rule — for example, "only black cards," or "cards must alternate between black and red," or "black cards must be even and red cards must be odd," etc.
Everyone else tries to figure out what the rule is. To do this, they play cards one at a time, and the person with the secret rule tells them whether or not each card follows their rule. (For example, if the rule is "black cards must be even and red cards must be odd," then if the people trying to guess the rule play the 4 of Spades, the person with the secret rule will tell them that that card does follow their rule, since it's an even black card.)
As you gather more data about which cards follow the rule and which cards don't, you can start to narrow down the possibilities for what the rule could be. How can you be strategic about playing cards that help you to find the rule?
In this activity, students play this game multiple times, with a different rule each time. The rules start simple but get more challenging!
Why we like this activity
- It’s fun! Students enjoy playing the game, as well as coming up with their own rules.
It requires students to engage in mathematical habits of mind:
- Making observations / comparing and contrasting / looking for patterns / finding and using strategies / making and testing predictions when trying to figure out the secret rule.
- It has a low floor and a high ceiling: It's easy for students to start playing the game and to figure out simpler rules, but as the rules get more complex, the game becomes more challenging!
This activity was developed in collaboration with the Julia Robinson Mathematics Festival.