Lesson 9
Using Tables for Conditional Probability
Lesson Narrative
The mathematical purpose of this lesson is for students to create and use twoway tables to estimate conditional probabilities, and to decide if events are independent. The work of this lesson connects to previous work because students investigated conditional probability and independence. The work of this lesson connects to upcoming work because students will continue to use probability to recognize dependent and independent events, and to practice finding probabilities for dependent and independent events. In the Math Talk activity, students have an opportunity to notice and make use of structure (MP7) when they recognize fraction bars as part of a fraction as well as representing division.
Technology isn't required for this lesson, but there are opportunities for students to choose to use appropriate technology to solve problems. We recommend making technology available.
Learning Goals
Teacher Facing
 Interpret (in written language) twoway tables to estimate probabilities including conditional probability.
 Use probabilities, including conditional probability, to justify (orally and in writing) that events are dependent or independent.
Student Facing
 Let’s use tables to estimate conditional probabilities.
Learning Targets
Student Facing
 I can estimate probabilities, including conditional probabilities, from twoway tables.
 I can use probabilities and conditional probabilities to decide if events are independent.
CCSS Standards
Glossary Entries

conditional probability
The probability that one event occurs under the condition that another event occurs.

dependent events
Dependent events are two events from the same experiment for which the probability of one event depends on whether the other event happens.

independent events
Independent events are two events from the same experiment for which the probability of one event is not affected by whether the other event occurs or not.