Classroom · Game Theory
Heads or tails, against someone who wants the opposite.
In every pair one player wins when the two calls match and the other when they differ. Everyone calls on their phone without seeing the other's call, the projector shows how the room called, and the same pairs call again having read it.
- In pairs
- About 30 min
- 2 acts
A practice run with fictional students. No real classroom or join code is created.
Try an answer on the phone. Lead the lesson from the screen.
On their phone
You are presenting
Setting up the room…
Lesson deck
Teach it as a ready-made lesson
Hook, how it works, the live game and takeaways. Edit anything.
Heads or tails?
A ready-to-teach lesson deck: a hook, how it works, the live game and takeaways for the debrief.
6 slides · 1 activity
What it teaches
Matching pennies is the textbook zero-sum game with no pure-strategy equilibrium, built from two players who want opposite things. Any lean toward heads or tails can be exploited by the other side, so the only unexploitable plan is to call each half the time. The second call shows whether a room can use a pattern it has seen, or hide its own.
- Zero-sum games
- Mixed strategies
- Nash equilibrium
Debrief, while the boards are still up
- 01
Did the room lean heads or tails the first time? Which side of each pair could have used that?
- 02
Matchers and mismatchers saw the same board. Should they have read it the same way?
- 03
What call could you announce in advance and still not be beaten on average?
- 04
Where else does one side win by reading the other, and the other by being unreadable?
How it works
- 01
Add it to your library
Sign up free and pull the activity from Decka's built-in classroom catalog — one click copies it into your own library, ready to run from Decka or inside PowerPoint.
- 02
Students join by QR
Everyone scans from the projector and plays in their phone's browser. No app, no account, nothing to install.
- 03
You run the room
You move the activity phase by phase: collection closes, the boards resolve on the big screen, and the debrief happens while the results are still up.
What is matching pennies in game theory?
Two players show a penny at the same moment. One takes both pennies when the faces match, the other when they differ. Whatever one side settles on, the other's best reply beats it, so the only equilibrium has both calling each face half the time.
Played live, roles are dealt as students join and stay fixed. Every call is blind, and pairs are dealt once the first call closes, one matcher and one mismatcher in each. The projector then shows how the whole room called, before the same pairs call again.
FAQ
Matching pennies questions, answered
How is this different from rock, paper, scissors?
Both are zero-sum with no pure-strategy equilibrium. Rock, paper, scissors gets there with three throws and identical players; matching pennies gets there with two calls and players who want opposite things.
How are roles given out?
By join order, and each student keeps their role for both calls. Pairs are dealt so that every pair has one matcher and one mismatcher.
What does the projector show?
How the whole room called, heads against tails, not split by role. It never shows who called what; each student sees their own result privately.
What is at stake?
By default, one penny a pair: the winner gains it and the loser gives it up. The payoffs are settings.
How long does it take?
Two calls; the saved default shows under the headline as "About N min", and every timer is a setting you control before you run it.
Do students need an app or an account?
No. Students scan a QR code from the projector (or open a link) and play in their phone's browser. Nothing to install and nothing to sign up for.
Does it work in PowerPoint or Google Slides?
In PowerPoint, yes: open the Decka add-in on a slide and choose the Classroom tile. Google Slides is not supported yet; there you present from Decka itself. Students play from their phones either way.
How many students can play at once?
Up to 50 participants per live activity on the free plan, 150 on Pro, and 300 on Badass.
More game theory games to run live
- Prisoner's dilemma — two suspects, separate rooms
- Twenty coins, take it or leave it
- Chicken — four seconds on a single-track lane
- The stag hunt — one day, two ways to spend it
- Battle of the sexes — one evening, two plans
- Ten rounds in the pot
- Rock, paper, scissors — two rivals and a contract
- All game theory activities
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