Waiting for a Double

Intent In this activity, students conduct their first simulation, collecting, displaying, and summarizing data to test a conjecture about probability. The activity draws upon their intuitive sense of probability and engages them in thinking more precisely about the topic. This is one of several activities in which intuitive notions about probability can be at odds with experimental or theoretical analyses.

Mathematics When rolling two dice, what is the average number of rolls needed to roll a double? In this activity, students approach this question through collecting and analyzing data. By rolling two dice repeatedly, they collect many examples of how many rolls it can take to get a double.

Progression Up to now, students have been exploring the unit problem informally. Now they begin a series of explorations designed to help them develop the tools they will need to answer the unit problem. The in-class portion of this activity has several parts: reviewing the homework, gathering class data, and graphing the class data.

Approximate Time 5 minutes for introduction 20 minutes for activity (at home or in class) 25 minutes to collect and analyze class data

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Key Questions Before assigning the activity: How would you do this experiment? Why is it important to get genuine data when doing activities like this? How do you compute the average of a set of numbers? During the class discussion: How did you make your prediction? What were the highest and lowest number of rolls you got? How might you graph one student’s outcomes? Can you visualize the average in terms of the graph? How might we graph the outcomes of the entire class? Is 1 a likely outcome?