Basic Probability Rules (Lesson 5.2)

Chapter 5 - Day 2

Learning Targets
  • Give a probability model for a chance process with equally likely outcomes and use it to find the probability of an event. 
  • Use the complement rule to find probabilities. 
  • Use the addition rule for mutually exclusive events to find probabilities. 
Activity: Who Will Win the Last Banana?

Experience First

This lesson was inspired by a presentation we saw from AP Stats all-star teacher Doug Tyson.


You will want to have dice ready (one for each student) and this video ready to go. Be sure to pause the video at 38 seconds!

Immediately after watching the intro, clarify with students the rules of the game and have them answer question #1 in the activity. You might even want to do a quick poll from the class to see how many students want to be Player 1 (most of them) and how many want to be Player 2 (probability masters).


Students will then play the game in pairs and the class will aggregate the results. This is the Law of Large Numbers in action…we should be getting closer and closer to the true probability as we play the game more and more. In the end, students use the sample space to discover that Player 2 has the advantage in this game.

Formalize Later

From a technical perspective, this lesson has perfect alignment between the learning targets, the experience, and the formalization that happens when debriefing the activity. While students don't have to know the fancy vocabulary as they work through the activity, there is plenty of opportunity for teachers to introduce these terms (Law of Large Numbers, complement rule, sample space) in the debrief of the activity.


Be sure to highlight the fact that the addition rule here only works for mutually exclusive events. We will investigate what happens when events are not mutually exclusive in Lesson 5.3 when we find the general addition rule.


After debriefing the activity, you can show the remaining 3 minutes in the video, which does a great chance of summarizing what students did in the activity, and even previews the idea of independent events, which we will study in Lesson 5.4 and Lesson 5.6.