ALEX Classroom Resource

  

Solving Linear Inequalities with Negative Numbers

  Classroom Resource Information  

Title:

Solving Linear Inequalities with Negative Numbers

URL:

https://aptv.pbslearningmedia.org/resource/mgbh.math.ee.inequality/solving-linear-inequalities-with-negative-numbers/

Content Source:

PBS
Type: Audio/Video

Overview:

Solve an inequality that has negative numbers and a variable. This video focuses on using inverse operations to solve for a variable and the importance of flipping the inequality when multiplying or dividing by a negative number. This video was submitted through the Innovation Math Challenge, a contest open to professional and nonprofessional producers.

Content Standard(s):
Mathematics
MA2019 (2019)
Grade: 6
18. Determine whether a value is a solution to an equation or inequality by using substitution to conclude whether a given value makes the equation or inequality true.
Unpacked Content
Evidence Of Student Attainment:
Students:
Given situations that have been modeled with equations or inequalities:
  • Substitute given specified values for the variables and the evaluate expressions.
  • Determine if the resulting numerical sentence is true when the specified values are substituted for the variables.
  • Explain with mathematical reasoning why a specified value is or is not a solution to a given equation or inequality.
Teacher Vocabulary:
  • Substitution
  • Equation
  • Inequality
Knowledge:
Students know:
  • Conventions of order of operations.
  • The solution is the value of the variable that will make the equation or inequality true.
  • That using various processes to identify the value(s) that when substituted for the variable will make the equation true.
Skills:
Students are able to:
  • Substitute specific values into algebraic equation or inequality and accurately perform operations of addition, subtraction, multiplication, division and exponentiation using order of operation.
Understanding:
Students understand that:
  • Solving an equation or inequality means finding the value or values (if any) that make the mathematical sentence true.
  • The solution to an inequality is often a range of values rather than a specific value.
Diverse Learning Needs:
Essential Skills:
Learning Objectives:
M.6.18.1: Define exponent, numerical expression, algebraic expression, variable, base, power, square of a number, and cube of a number.
M.6.18.2: Compute a numerical expression with exponents, with or without a calculator.
M.6.18.3: Restate exponential numbers as repeated multiplication.
M.6.18.4: Choose the correct value to replace each variable in the expression (Substitution).
M.6.18.5: Calculate the multiplication of single or multi-digit whole numbers, with or without a calculator.

Prior Knowledge Skills:
  • Use comparison symbols.
    Examples: >, =, or < .
  • Record the results of comparisons with the symbols >, =, or <, and justify the conclusions, e.g., by using a visual fraction model.
  • Compare two three-digit numbers based on meanings of the hundreds, tens, and ones digits using >, =, and < symbols to record the results of comparisons.
  • Comparison symbols.
    Examples: >, =, and < .
  • Compare two three-digit numbers based on meanings of the hundreds, tens, and ones digits using >, =, and < symbols to record the results of comparisons.
  • Compare two fractions with the same numerator or the same denominator by reasoning about their size.
  • Recognize that comparisons are valid only when the two fractions refer to the same whole.
  • Record the results of comparisons with the symbols >, =, or <, and justify the conclusions, e.g., by using a visual fraction model.
  • Convert fractions to decimals.
  • Compare two decimals to tenths.
  • Compare whole numbers.
  • Identify comparison symbols.
    Examples: >, <, and = .

Alabama Alternate Achievement Standards
AAS Standard:
M.AAS.6.19 Match equations and inequalities to real-world situations.


Mathematics
MA2019 (2019)
Grade: 7
9. Use variables to represent quantities in real-world or mathematical problems and construct algebraic expressions, equations, and inequalities to solve problems by reasoning about the quantities.

a. Solve word problems leading to equations of the form px + q = r and p(x + q) = r, where p, q, and r are specific rational numbers. Solve equations of these forms fluently. Compare an algebraic solution to an arithmetic solution, identifying the sequence of the operations used in each approach.

b. Solve word problems leading to inequalities of the form px + q > r or px + q < r, where p, q, and r are specific rational numbers. Graph the solution set of the inequality, and interpret it in the context of the problem.
Unpacked Content
Evidence Of Student Attainment:
Students:
  • Write and solve mathematical equations (or inequalities) to model real-world problems.
  • Interpret the solution to an equation in the context of a problem
  • Interpret the solution set of an inequality in the context of a problem.
  • Graph the solution to an inequality on a number line.
Teacher Vocabulary:
  • Algebraic expressions
  • Equations
  • Inequalities
  • Greater than
  • Greater than or equal to
  • less than
  • less than or equal to
Knowledge:
Students know:
  • p(x + q) = px + pq, where p and q are specific rational numbers.
  • When multiplying or dividing both sides of an inequality by a negative number, every term must change signs and the inequality symbol reversed.
  • In the graph of an inequality, the endpoint will be a closed circle indicating the number is included in the solution set (≤ or ≥) or an open circle indicating the number is not included in the solution set ( < or >).
Skills:
Students are able to:
  • use variables to represent quantities in a real-world or mathematical problem.
  • Construct equations (px + q = r and p(x + q) = r) to solve problems by reasoning about the quantities.
  • Construct simple inequalities (px + q > r or px + q < r) to solve problems by reasoning about the quantities.
  • Graph the solution set of an inequality.
Understanding:
Students understand that:
  • Real-world problems can be represented through algebraic expressions, equations, and inequalities.
  • Why the inequality symbol reverses when multiplying or dividing both sides of an inequality by a negative number.
Diverse Learning Needs:
Essential Skills:
Learning Objectives:
M.7.9.1: Define equation, inequality, and variable.
M.7.9.2: Set up equations and inequalities to represent the given situation, using correct mathematical operations and variables.
M.7.9.3: Calculate a solution or solution set by combining like terms, isolating the variable, and/or using inverse operations.
M.7.9.4: Test the found number or number set for accuracy by substitution.
M.7.9.5: Recall solving one step equations and inequalities.
M.7.9.6: Recognize properties of numbers (Distributive, Associative, Commutative).
M.7.9.7: Define equation and variable.
M.7.9.8: Set up an equation to represent the given situation, using correct mathematical operations and variables.
M.7.9.9: Calculate a solution to an equation by combining like terms, isolating the variable, and/or using inverse operations.
M.7.9.10: Test the found number for accuracy by substitution.
Example: Is 5 an accurate solution of 2(x + 5)=12?.
M.7.9.11: Identify the unknown, in a given situation, as the variable.
M.7.9.12: List given information from the problem.
M.7.9.13: Recalling one-step equations.
M.7.9.14: Explain the distributive property.
M.7.9.15: Define inequality and variable.
M.7.9.16: Set up an inequality to represent the given situation, using correct mathematical operations and variables.
M.7.9.17: Calculate a solution set to an inequality by combining like terms, isolating the variable, and/or using inverse operations.
M.7.9.18: Test the solution set for accuracy.
M.7.9.19: Identify the unknown, of a given situation, as the variable.
M.7.9.20: List information from the problem.
M.7.9.21: Recall how to graph inequalities on a number line.
M.7.9.22: Recall how to solve one step inequalities.

Prior Knowledge Skills:
  • Define inequality.
  • Define equivalent, simplify, term, distributive property, associative property of addition and multiplication, and the commutative property of addition and multiplication.
  • Define equation, solution of an equation, solution of an inequality, and inequality.
  • Compare and contrast equations and inequalities.
  • Determine if an inequality is by replacing the variable with a given number.
  • Determine if an equation is true by replacing the variable with a given number.
  • Simplify a numerical sentence to determine equivalence.
  • Recognize the symbols for =, >, <, ?, and ?.
  • Define equation and variable.
  • Set up an equation to represent the given situation, using correct mathematical operations and variables.
  • Identify the unknown, in a given situation, as the variable.

Alabama Alternate Achievement Standards
AAS Standard:
M.AAS.7.9 Use the properties of operations to solve one-step equations and inequalities from real-world and mathematical problems.


Mathematics
MA2019 (2019)
Grade: 7
Accelerated
18. Use variables to represent quantities in a real-world or mathematical problem and construct algebraic expressions, equations, and inequalities to solve problems by reasoning about the quantities.

a. Solve word problems leading to equations of the form px + q = r and p(x + q) = r, where p, q, and r are specific rational numbers. Solve equations of these forms fluently. Compare an algebraic solution to an arithmetic solution, identifying the sequence of the operations used in each approach.

b. Solve word problems leading to inequalities of the form px + q > r or px + q < r, where p, q, and r are specific rational numbers. Graph the solution set of the inequality and interpret it in the context of the problem.
[Grade 7, 9, and linear portion of Algebra I with Probability, 11]
Unpacked Content
Evidence Of Student Attainment:
Students:
  • Write and solve mathematical equations (or inequalities) to model real-world problems.
  • Interpret the solution to an equation in the context of a problem.
  • Interpret the solution set of an inequality in the context of a problem.
Teacher Vocabulary:
  • Algebraic expressions
  • Equations
  • Inequalities
  • Greater than
  • Greater than or equal to
  • less than
  • less than or equal to
Knowledge:
Students know:
  • p(x + q) = px + pq, where p and q are specific rational numbers.
  • When multiplying or dividing both sides of an inequality by a negative number, every term must change signs and the inequality symbol reversed.
  • In the graph of an inequality, the endpoint will be a closed circle indicating the number is included in the solution set (≤ or ≥) or an open circle indicating the number is not included in the solution set ( < or >).
Skills:
Students are able to:
  • Use variables to represent quantities in a real-world or mathematical problem.
  • Construct equations (px + q = r and p(x + q) = r) to solve problems by reasoning about the quantities.
  • Construct simple inequalities (px + q > r or px + q < r) to solve problems by reasoning about the quantities.
  • Graph the solution set of an inequality.
Understanding:
Students understand that:
  • Real-world problems can be represented through algebraic expressions, equations, and inequalities.
  • The inequality symbol reverses when multiplying or dividing both sides of an inequality by a negative number, and why.
Diverse Learning Needs:
Tags: greater than, inequality, inverse, less than, variable
License Type: Public Domain
For full descriptions of license types and a guide to usage, visit :
https://creativecommons.org/licenses
AccessibilityVideo resources: includes closed captioning or subtitles
Comments

Additional support materials are located under Support Materials for Teachers in the upper right-hand corner of the webpage. 

  This resource provided by:  
Author: Kristy Lacks
Alabama State Department of Education