Probability

Lesson 5

Math

Unit 8

10th Grade

Lesson 5 of 10

Objective


Describe conditional probability and develop the rule $$P(B|A)=\frac{P(A \space \mathrm{and} \space B)}{P(A)}$$.

Common Core Standards


Core Standards

  • S.CP.A.3 — Understand the conditional probability of A given B as P(A and B)/P(B), and interpret independence of A and B as saying that the conditional probability of A given B is the same as the probability of A, and the conditional probability of B given A is the same as the probability of B.

Foundational Standards

  • 7.SP.C.5

Criteria for Success


  1. Describe conditional probability as the probability of a subsequent event occurring if you already know what has been chosen as the primary event. 
  2. Use the notation $$P(B|A)$$ to represent conditional probability.
  3. Develop the rule $$ P(B│A)=\frac{P(A \space and \space B)}{P(A)}$$ for calculating the conditional probability.
  4. Describe why the formula for calculating conditional probability makes sense. 

Tips for Teachers


Fishtank Plus

Unlock features to optimize your prep time, plan engaging lessons, and monitor student progress.

Anchor Problems


Problem 1

There are four red envelopes, four blue envelopes, and four $1 bills, which will be placed in four of the eight envelopes. Suppose one $1 bill is placed in a blue envelope and the three remaining $1 bills are placed in three red envelopes. 

  1. If you choose a blue envelope, what is the probability that you will get the $1?
  2. If you choose a red envelope, what is the probability that you will get the $1?

Below is a tree diagram you can use to answer the questions. Write in the probabilities as described above.

Guiding Questions

Create a free account or sign in to access the Guiding Questions for this Anchor Problem.

References

Illustrative Mathematics Lucky Envelopes

Lucky Envelopes, accessed on June 15, 2017, 8:49 a.m., is licensed by Illustrative Mathematics under either the CC BY 4.0 or CC BY-NC-SA 4.0. For further information, contact Illustrative Mathematics.

Modified by Fishtank Learning, Inc.

Problem 2

Suppose the $1 bills are redistributed among the envelopes. Two $1 bills are placed in two blue envelopes and two $1 bills are placed in two red envelopes. Record the probabilities on the tree diagram. 

  1. What is the probability, if you choose a blue envelope, that you will get the $1?
  2. What is the probability, if you choose a red envelope, that you will get the $1?

Guiding Questions

Create a free account or sign in to access the Guiding Questions for this Anchor Problem.

References

Illustrative Mathematics Lucky Envelopes

Lucky Envelopes, accessed on June 15, 2017, 8:49 a.m., is licensed by Illustrative Mathematics under either the CC BY 4.0 or CC BY-NC-SA 4.0. For further information, contact Illustrative Mathematics.

Modified by Fishtank Learning, Inc.

Problem 3

Data gathered on the shopping patterns during the months of April and May of high school students from Peanut Valley revealed the following. 38% of students purchased a new pair of shorts (call this event $$H$$), 15% of students purchased a new pair of sunglasses (call this event $$G$$), and 6% of students purchased both a pair of shorts and a pair of sunglasses. Find the probability that a student purchased a pair of sunglasses given that you know they purchased a pair of shorts. 

Guiding Questions

Create a free account or sign in to access the Guiding Questions for this Anchor Problem.

References

Mathematics Vision Project: Geometry Module 8: ProbabilityLesson 6 "Go" (p. 28, #9)

Module 8: Probability from Geometry: A Learning Cycle Approach made available by Mathematics Vision Project under the CC BY 4.0 license. © 2016 Mathematics Vision Project. Accessed Sept. 20, 2018, 10:11 a.m..

Target Task


Create a situation where $$P(A|B) = P(A)$$.

Additional Practice


The following resources include problems and activities aligned to the objective of the lesson that can be used for additional practice or to create your own problem set.

  • Use any of the previous Anchor Problem examples to create conditional probability problems.
icon/arrow/right/large copy

Lesson 4

icon/arrow/right/large

Lesson 6

Lesson Map

A7CB09C2-D12F-4F55-80DB-37298FF0A765

Topic A: Conditional Probability and the Rules of Probability

Request a Demo

See all of the features of Fishtank in action and begin the conversation about adoption.

Learn more about Fishtank Learning School Adoption.

Contact Information

School Information

What courses are you interested in?

ELA

Math

Are you interested in onboarding professional learning for your teachers and instructional leaders?

Yes

No

Any other information you would like to provide about your school?

Effective Instruction Made Easy

Effective Instruction Made Easy

Access rigorous, relevant, and adaptable math lesson plans for free