Probability

Lesson 4

Math

Unit 8

10th Grade

Lesson 4 of 10

Objective


Determine the probability of events that are not mutually exclusive to formalize the addition rule.

Common Core Standards


Core Standards

  • S.CP.A.1 — Describe events as subsets of a sample space (the set of outcomes) using characteristics (or categories) of the outcomes, or as unions, intersections, or complements of other events ("or," "and," "not").
  • S.CP.A.2 — Understand that two events A and B are independent if the probability of A and B occurring together is the product of their probabilities, and use this characterization to determine if they are independent.
  • S.CP.B.7 — Apply the Addition Rule, P(A or B) = P(A) + P(B) - P(A and B), and interpret the answer in terms of the model.

Foundational Standards

  • 7.SP.C.5
  • 7.SP.C.6

Criteria for Success


  1. Describe what it means for an event to overlap with another—that is, the probability of $$P(A \space or \space B)$$ includes $$ P(A \space and \space B)$$.
  2. Use a Venn diagram to describe the sample space of a chance experiment when events overlap and identify $$P(A)$$, $$P(A \space or \space B)$$, $$P(not A)$$, and $$P(A \space and \space B)$$.
  3. Calculate the compound probability of an overlap event by multiplying the probability of the individual outcomes. 
  4. Calculate the probability of an overlap event of $$P(A \space or \space B)=P(A)+P(B)-P(A \space and \space B)$$ and describe that the rule is derived from the understanding that the probability of an “or” event should only count each outcome once and that subtracting the “and” ensures this.
  5. Describe a complement of event $$A$$ as the mutually exclusive event of $$A$$ not happening so that the sum of the probabilities of an event and its complement equals 1. 

Tips for Teachers


This lesson introduces Venn diagrams to visualize probabilities. Venn diagrams are useful strategies for students to understand when events are mutually exclusive and when they are not. Each section of a two-circle Venn diagram (only, and, only, not) represents a separate branch on a tree diagram. It is not necessary for students to convert from one to the other, but important for students to be able to choose a visual representation that makes sense and use it appropriately. 

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Anchor Problems

25-30 minutes


Problem 1

At a particular diner, everyone drinks coffee. However, some people drink their coffee with sugar, some with cream, some with both, and some with neither.

Describe the coffee preferences of the 30 people in the diner in the Venn diagram below. Be sure to label the circles appropriately.

  • 10 people just like cream in their coffee.
  • 13 people like sugar in their coffee; 8 of these people also like cream.
  • 7 people like neither cream nor sugar in their coffee.

Guiding Questions

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Problem 2

Below is a diagram that shows all of the members of the student council at a particular high school. Each member is represented by a labeled point. The students that are in circle “$$J$$” are juniors and the students in circle “$$M$$” are male.

  1. Find $$P(J)$$.
  2. Find $$P(M)$$.
  3. Find $$P(J \space and \space M)$$.
  4. Find $$P(J \space or \space M)$$.
  5. Why does $$ P(J \space or \space M)≠P(J)+P(M)$$? Design a formula to calculate $$P(J \space or \space M)$$ using any of the probability found in (a) through (c).

Guiding Questions

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References

Illustrative Mathematics The Addition Rule

The Addition Rule, accessed on June 15, 2017, 8:42 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.

Target Task

5-10 minutes


At Mom’s diner, everyone drinks coffee. Let $$C$$ be the event that a randomly selected customer puts cream in their coffee. Let $$S$$ be the event that a randomly selected customer puts sugar in their coffee. Suppose that after years of collecting data, Mom has estimated the following probabilities:

$$P(C)=0.6$$
$$P(S)=0.5$$
$$P(C \space or \space S)=0.7$$

Estimate $$ P(C \space and \space S)$$ and interpret this value in the context of the problem.

References

Illustrative Mathematics Coffee at Mom's Diner

Coffee at Mom's Diner, accessed on June 15, 2017, 8:48 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.

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.

  • Include problems that extend Anchor Problems #1 and #2. For example, “What is the probability that you choose two random people in the diner and both of them like cream and sugar in their coffee?” or “What is the probability that two students on the student council who are chosen on different weeks to make the announcements are female one week and male and not a junior on the second week?”

Next

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

Lesson 5
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Lesson Map

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

Topic A: Conditional Probability and the Rules of Probability

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