Linear Expressions & Single-Variable Equations/Inequalities

Lesson 10

Math

Unit 3

9th Grade

Lesson 10 of 12

Objective


Solve unbounded single-variable inequalities in contextual and non-contextual situations.

Common Core Standards


Core Standards

  • A.CED.A.3 — Represent constraints by equations or inequalities, and by systems of equations and/or inequalities, and interpret solutions as viable or nonviable options in a modeling context. For example, represent inequalities describing nutritional and cost constraints on combinations of different foods.
  • A.REI.A.1 — Explain each step in solving a simple equation as following from the equality of numbers asserted at the previous step, starting from the assumption that the original equation has a solution. Construct a viable argument to justify a solution method.
  • A.REI.B.3 — Solve linear equations and inequalities in one variable, including equations with coefficients represented by letters.
  • A.SSE.B.3 — Choose and produce an equivalent form of an expression to reveal and explain properties of the quantity represented by the expression. Modeling is best interpreted not as a collection of isolated topics but in relation to other standards. Making mathematical models is a Standard for Mathematical Practice, and specific modeling standards appear throughout the high school standards indicated by a star symbol (★). The star symbol sometimes appears on the heading for a group of standards; in that case, it should be understood to apply to all standards in that group.

Foundational Standards

  • 7.EE.B.4.B

Criteria for Success


  1. Describe an inequality as a constraint on a situation. 
  2. Describe the maximum, the minimum, and some additional values that are solution sets of a one-variable inequality. 
  3. Write more than one inequality from a solution presented graphically on a number line, given particular constraints. 
  4. Solve a single-variable inequality using negative and positive rational number coefficients. 
  5. Describe why "flipping the inequality" is necessary when solving by a negative coefficient—through understanding testing points and identifying true and untrue statements.

Tips for Teachers


  • This lesson will prepare students to access A-CED.3, solving inequalities, and is an extension of the 7th grade standard, 7.EE.4b. 
  • This lesson ensures that students have a solid foundation in the uses and mechanics of single-variable, unbounded inequalities before they study compound inequalities in the next lesson. 
  • This lesson does not explicitly ask students to write an algebraic inequality from a graphical representation. Ensure that students are practicing this skill in the problem set. 
  • A strategy that would be useful for students to practice is sketching a number line with benchmark numbers to show relative location. For example, if $${\frac{5}{2}}$$ is being graphed as an endpoint, mark this value as well as 0 and 2 and 4 (or 0, 1, 2, 3). This ensures that students are grasping the value of the number they are graphing but not spending a lot of time creating a number line. 
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Anchor Problems

25-30 minutes


Problem 1

Rewrite the given “word sentence” as a “math sentence.” Each math sentence will use one of the following symbols: $${> , < , \leq , \geq }$$. Use $$x$$ in place of the number.

  • A number greater than 13 
  • A number that is at least 13 
  • A number that is no fewer than 13 
  • A number that is at most 13 
  • A number that is fewer than 13 
  • A number that is not above 13 
  • A number that is no more than 13

Guiding Questions

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Problem 2

Jonathan wants to save up enough money so that he can buy a new sports equipment set that includes a football, baseball, soccer ball, and basketball. This complete boxed set costs $50. Jonathan has $15 he saved from his birthday. In order to make more money, he plans to wash neighbors’ windows. He plans to charge $3 for each window he washes, and any extra money he makes beyond $50 he can use to buy the additional accessories that go with the sports box set. 

Write an inequality that describes the amount of money that Jonathan would like to earn washing windows towards the cost of the sports boxed set.

Guiding Questions

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References

Illustrative Mathematics Sports Equipment Set

Sports Equipment Set, accessed on Aug. 31, 2017, 4:22 p.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.

Problem 3

How is the solution set to the inequality $${5q+10>20}$$ different than the solution set for the inequality $$ -{5q+10>20}$$

Justify your reasoning by providing solutions to both inequalities algebraically, graphically, and in words.

Guiding Questions

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References

EngageNY Mathematics Algebra I > Module 1 > Topic C > Lesson 14Example 1

Algebra I > Module 1 > Topic C > Lesson 14 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Problem Set

15-20 minutes


Give your students more opportunities to practice the skills in this lesson with a downloadable problem set aligned to the daily objective.

Target Task

5-10 minutes


Problem 1

Find the solution to the following inequality. Express your solution algebraically and graphically.

$${6x-5<7x+4}$$

References

EngageNY Mathematics Algebra I > Module 1 > Topic C > Lesson 14Exit Ticket

Algebra I > Module 1 > Topic C > Lesson 14 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

Problem 2

Fergus was absent for today’s lesson and asked Mike to explain why the solution to $${-5x>30}$$ is $${x<-6}$$. Mike said, “Oh! That’s easy. When you multiply by a negative, just flip the inequality.” Provide a better explanation to Fergus about why the direction of the inequality is reversed.

References

EngageNY Mathematics Algebra I > Module 1 > Topic C > Lesson 14Exit Ticket

Algebra I > Module 1 > Topic C > Lesson 14 of the New York State Common Core Mathematics Curriculum from EngageNY and Great Minds. © 2015 Great Minds. Licensed by EngageNY of the New York State Education Department under the CC BY-NC-SA 3.0 US license. Accessed Dec. 2, 2016, 5:15 p.m..

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 where students need to write an inequality from a solution that is presented graphically. Identify more than one possible inequality for the situation.

Next

Write and graph compound single-variable inequalities to describe the solution to contextual and non-contextual situations.

Lesson 11
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Lesson Map

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

Topic A: Properties and Solutions of Single-Variable Linear Expressions and Equations

Topic B: Modeling with Single-Variable Linear Equations

Topic C: Properties and Solutions of Single-Variable Linear Inequalities

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