Algebra 2 Note-taking Guide
Algebra 2 - Lesson 9.03 Conditional Probability
Please print this out in advance, and as you are working through the lesson, fill in the information and use this as your notes.
 The goal is to have all the empty boxes checked
Use this set of arrows
to guide you through
the lesson
As you complete this lesson, please check that you can answer:
 How can you explain the concepts of conditional probability and independence in everyday situations?
 How can you find the conditional probability of A given B as the fraction of B’s outcomes that also belong to A, and
interpret the answer in terms of the model?
 How can you apply the Addition Rule and interpret the answer in terms of the model?
Conditional Probability (page 2)
Recall that two events are ____________________ if knowledge of the first outcome does not affect the probability
of the second outcome.
When two events are not independent, rules for conditional probability will apply. From the last lesson, you already
know how to find conditional probability using the probability of each event.
Use the space below to complete examples 1 and 2. Pay close attention to how the probability is interpreted
in the context of the problem.
Example 1:
Algebra 2 Notetaking Guide
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Example 2:
Interpreting Probability (page 2)
The two-way frequency table below shows the education level and employment status of 242,714 people. A person
is randomly selected from this group.
Employed
Self-Employed
Unemployed
Total
Did not graduate high school
8,252
2,052
3,562
13,866
High school graduate
45,083
9,151
9,512
63,746
Attended college or tech school
48,245
9,778
7,833
65,856
College or tech school graduate
77,010
16,069
6,167
99,246
Total
178,590
37,050
27,074
242,714
Use the space below to answer this question:
Probability of Unions and Intersections (page 3)
Review the two-way frequency table and answer the questions that follow it:
Employed
SelfEmployed
Did not graduate high school
8,252
2,052
3,562
13,866
High school graduate
45,083
9,151
9,512
63,746
Attended college or tech school
48,245
9,778
7,833
65,856
College or tech school graduate
77,010
16,069
6,167
99,246
Total
178,590
37,050
27,074
242,714
Algebra 2 Notetaking Guide
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Unemployed
Total
This leads to a new rule for probability of unions:
Use the space below to complete examples 1 and 2:
Example 1:
Example 2:
Events that cannot possibly happen together are called ____________________ ___________________ events.
Complete the sorting activity on page 3 to practice identifying mutually exclusive events.
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Remember that the formula for P(A U B) = P(A) + P(B) − P(A ∩ B), but with mutually exclusive events, P(A ∩ B) = 0
since A and B will have no outcomes in common. Therefore, with mutually exclusive events, P(A U B) = P(A) + P(B).
Use the space below to complete example 3:
Practice (page 4)
Finally, complete the 9.03 Assessment, Conditional Probability. This is an auto-graded assignment. You will
get immediate feedback on your work.
Algebra 2 Notetaking Guide
Version 14
Florida Virtual School