Abstract
This lesson is designed to improve students' understanding of decision making
strategies by introducing students to basic probability.
Standards (NCTM)
Data Analysis
Understand and apply basic concepts of probability
 understand and use appropriate terminology to describe complementary
and mutually exclusive events
 use proportionality and a basic understanding of probability to make
and test conjectures about the results of experiments and simulations
Student Prerequisites
 Educational:
Students should know:
 basic concept of data sets/collection.
 basic statistical concepts and measures
 Technological:
Students must be able to:
 perform basic mouse manipulations such as point,
click and drag.
 use a browser such as Netscape for experimenting with
the activities.
Teacher Preparation
Teachers will need:
Students will need:
 access to a browser.
 pencil and paper.
Lesson Outline
 Focus and Review
 Have students discuss the chance that a fair coin will land on heads if
it's flipped.
 Present the students with the
Birthday Problem.
Ask them: "What is the probability you will share a birthday with someone in this room?"
 After giving the students time to figure out the problem, walk the class through the solution.
 Inform the class that today they are going to learn about different types of probabilities and how they relate to game theory.
 Objectives
 Students will be introduced to the concept of proportionality.
 Guided Practice
 Split the students into groups of two or more.
 Hand out the bags of M&Ms  one for each group.
 Students should:
 Count the M&M's in their bag by color.
 Record the results on a piece of paper.
 Record the total number of M&M on the same piece of paper.
 Have students draw 60 M&M's with replacement and record the results by color.
 After they finish ask them to calculate the proportion of M&M's drawn of each
color.
 Teacher Input
 Discuss how the groups' experimental results could be
different from the theoretical probabilities.
 Discuss the fact that knowledge of previous trials does not affect the
probability of getting a heads on subsequent trials. Introduce this type
of event as an independent event.
 Discuss how the results could be different if the students did not
replace the M&M's
Guided Practice
 Split students up into groups of two or more.
 Hand out the Conditional Probability Data Sheet.
 Specify the number of times students will need to repeat the procedure.
 Allow students time to work through the activity.
 Upon finishing, let students further explore this concept by playing
with the Marbles applet. Make sure the set up is the same as it was for
the Conditional Probability Exercise.
Teacher Input
 Does each combination have the same probability of being drawn? Which
combinations have a smaller chance and why?
 Give formal definitions of notation for the probability of an event, the
probability of its complement, and its conditional probability  the probability that event A will
occur based on the fact that event B has already occured.
Teacher Input
 Refer back to the brain teaser
about the common birthdays and explain that the question can be
answered with conditional probabilities.
Guided Practice
 Have pairs of students run sets of 1000 trials for groups of different sizes
with the
Birthday Problem Activity.
 After collecting each groups data, graph the probablity of repeated birthdays
as a function of number of people in the group.
Teacher Input
 Explain Bayes Theorem.
 Address how it applies to game theory.
 Run through the
Bayes Theorem activity with the class to illustrate this point.
Guided Practice
 Allow students to experiment with the
Bayes Theorem
activity by entering in different values to observe the effects
of changing the various probabilities on the situation.
 Have students record the trends they notice on a piece of paper.
 After explaining how the activity uses Bayes Theorem to predict your next move,
allow students to play the
RockPaperScissors game.
 Again students should note any trends they notice while playing the game.
Teacher Input
 Review/Define basic probability notation
 Pose the question of the Prisoner's Dilemma:
Imagine two criminals arrested under the suspicion of having
committed a crime together. However, the police do not
have sufficient proof to convict them. The two
prisoners are isolated from each other; the police visit
each of them and offer a deal: they will receive a reduced sentence
if they rat on their partner. If neither criminal accepts the
the offer, there is only enough evidence to convict each of them for
5 years. If only one criminal offers evidence, he goes to prison for
1 year and his partner will go to prison for 10 years. However if
both criminals take the deal, each of them will get the maximum number of years,
because the deals are null and void after enough evidence has been gathered to
convict the criminals.

Prisoner 1 
Prisoner 2 

Stay Silent 
Take Deal 
Stay Silent 
5 , 5 
10 , 1 
Take Deal 
1 , 10 
10 , 10 
 Discuss the idea of game theory as optimization of strategies.
 Independent Practice
 Allow students to play through the
Friends and Fortunes Activity while carefully considering
whether to use aggressive or conservative strategies.
 Have students try the game again using different strategies.
 Closure
 Discuss the results of the Friends and Fortunes game and the different
strategies the students used.
 Lead a discussion about the
Magnet Schools article and how it applies to game theory.

