Reason for Alignment: The lesson Tree Diagrams shows students how to draw a tree diagram for multi-stage events and how to use tree diagrams to compute probability. Note: the textbook calls these problems Multistage Experiments while the terminology in the Interactivate lesson is Compound Events.
Reason for Alignment: Since the textbook also looks at tree diagrams as a tool to show possible outcomes. There is a detailed discussion of trees as data structures in the lesson.
Arithmetic: Student must be able to:
add and multiply fractions.
Technological: Students must be able to:
perform basic mouse manipulations such as point, click and drag.
use a browser for experimenting with the activities.
Access to a browser
Pencil and paper
Two or more events that happen simultaneously
Conditional probability is the probability of an event occurring given that another event also occurs. It is expressed as P(A/B). It reads "Probability of Event A on condition of Event B." P(A/B) = P(A and B)/P(B), where P(B) is the probability of event B and P(A and B) is the joint probability of A and B
Focus and Review
Remind students what has been learned in previous lessons such as concepts of probability.
Possibly use the example of rolling a die and the chances of that die rolling a specific number is
1/6. Ask students what the probability is of rolling a 1
or a 2. Mention the difference between the experimental probability and the theoretical probability.
You can even have the students roll dice themselves, collect data for the class and figure the
experimental probability for the class.
Let the students know what it is they will be doing and learning today. Say something like this:
Today, class, we will be talking more about probability and how to determine the probability
of multiple events, known as compound events. We will learn how to create tree diagrams to
determine the probabilities related to compound events.
We are going to use the computers but please do not turn your computers on until I ask you to.
I want to show you a little about the program first.
Demonstrate some of the functionality yourself such as changing the length of the race,
changing the game to an unfair race, and demonstrating how the multiple run panel works.
Discuss and draw a tree diagram for a one-step and a two-step fair race. If you have a white board
it is helpful to use a red and a blue marker to represent the two different colored cars.
Make the race an unfair race by making the blue car move on rolls of 1 and 2 and the red car move
on rolls of 3, 4, 5, and 6.
Draw a tree diagram for a one-step unfair race. Mention that the sum of the end probabilities
always equal one, which makes them complementary probabilities. Discuss why this must be so.
Ask the students to go to their computers and create an unfair race as described above. In the
multiple-run panel change the number of runs to 50,000. Have students run this configuration 5 or
6 times. Ask them to develop a hypothesis as to what the theoretical probability of an unfair
two-step is based on the experimental data using the applet.
Have the students create a tree diagram for an unfair two-step race to determine the theoretical
Have them show, based on their diagrams, the sum of the final probabilities equal one
demonstrating they are complementary probabilities.
You may wish to bring the class back together for a discussion and verification of their findings.
Once the students have been allowed to share what they found, summarize the results of the lesson.
If there is only one available computer, place the students in groups of two or three. Run the
multiple races yourself and have them develop the hypothesis with their partners.