Semi-Mathy Games

Here are some silly semi-mathy things I’ve done with my students either as bonus problems or fillers.  I cannot vouch for their pedagogical value.

  • +1 or +3.  A bonus question appeared at the end of a test.  “Write Free +1 and you’ll get a bonus point on the test, no questions asked.  Or write Go For +3 and if two-thirds of the class does it, all who do will get 3 bonus points.  Saying anything out loud voids the bonus for everyone.”  I was pretty surprised that in most classes, not enough students went for the +3.  One student wrote Free +3 and got nothing…
  • Choose A or B.  In class, students were given this choice: “Write A and you’ll get a point for everyone in the class who writes A.  Write B and you’ll get twice as much as anyone who writes A.”  After a long debate, most students picked B.  Far fewer students picked B when the choices were revealed publicly instead of privately.  (Social commentary followed…)
  • The probability you’ll get this question right.  Still one of my favorite bonus problems of all time, this came from my wife: “If train A leaves Denver at 50 miles per hour, and train B leaves Chicago at 60 miles per hour, what is the probability that you’ll get this question right?”  Students who wrote 1 or 100% were right, students who wrote 0 were wrong, and anything in between was resolved with a coin or random number generator.  (There’s a fun discussion over whether a student who writes 0 can be right by being wrong… but if they’re right then they’re wrong…)
  • The dollar auction.  This one is evil.  See for a full description.  In one class, a student successfully “escaped” by outbidding the other player significantly.   In another class, a third student jumped into the auction midstream allowing another to escape.  If I were still teaching, I would repeat the process using the bidding systems by Beezid and other “penny auction” sites (  Hopefully by exploring these auction styles with students they will avoid being scammed for real money later in life.

What else?


About Bowen Kerins
Bowen is a mathematics curriculum writer. He is a lead author of CME Project, a high school curriculum focused on mathematical habits of mind. Bowen leads professional development nationally, primarily on how math content can be taught with a focus on higher-level goals. Bowen is also a champion pinball player and once won $1,000 for knowing the number of degrees in a right angle.

4 Responses to Semi-Mathy Games

  1. Mimi says:

    Fun!:) Thanks for sharing!

  2. Nathan says:

    I sometimes use a prisoner’s dilemma type game that I stole from a Yale game theory course:

    “At the bottom of your test, write the letter α or β. Extra credit will be determined as follows: I will randomly pair your test with one other person from the class and

    1) Give you both 1 point if both tests are marked with a α.
    2) Give you both 2 points if both tests are marked with a β
    3) Give the person who marked β 0 points and the person who marked α 3 points if the tests are marked differently.”

    By the way, are you planning on attending ICME in Korea this year?

    • Bowen Kerins says:

      This seems a little unfair, since your random pairing causes a lot of the variance. I guess I’d have to mark alpha if I didn’t know what I was being compared to, because I’m guaranteed at least 1 point and an “average” of 2 (if I assume everyone else splits 50/50). Meanwhile if I mark beta, my maximum possible is 2 and my “average” is 1.

      Another way to do this that doesn’t involve randomness is to compare your test to the majority of the class:

      0) You get 0 points if you mark beta and the majority of the class marks alpha
      1) You get 1 point if you mark alpha and the majority of the class also marks alpha
      2) You get 2 points if you mark beta and the majority of the class also marks beta
      3) You get 3 points if you mark alpha and the majority of the class marks beta

      This makes the “beta is cooperative” very clear: by marking beta you can give the entire class at least 2 points (if enough people join in).

      Never been to ICME, someday perhaps. I’ll be at the AMS/MAA Joint Meetings in Boston this week.

  3. Fawn Nguyen says:

    These are fun! For the second game, you wrote, “Far fewer students picked B when the choices were revealed publicly instead of privately.” Not sure I understand how the game would work if choices were made known to everyone.
    I agree, I would definitely mark alpha in the Yale game since it has, for reasons you stated, better odds.

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