Numerical and Algebraic Expressions

Lesson 6

Math

Unit 3

7th Grade

Lesson 6 of 11

Objective


Subtract and simplify expressions.

Common Core Standards


Core Standards

  • 7.EE.A.1 — Apply properties of operations as strategies to add, subtract, factor, and expand linear expressions with rational coefficients.

Foundational Standards

  • 6.EE.A.3
  • 6.EE.A.4
  • 7.NS.A.1
  • 7.NS.A.2

Criteria for Success


  1. Understand that when an expression is subtracted, every term in the expression is subtracted.
  2. Understand that subtracting an expression is the same as distributing a $${-1}$$ through the parentheses group, changing the sign of each term. 
  3. Subtract and simplify expressions.

Tips for Teachers


This lesson includes problems such as $${3x - (6 + 8x) }$$ but does not include problems such as $${3x - 2(6 + 8x)}$$, where a multiple of an expression is being subtracted. This will be covered in Lesson 7 and Lesson 8. The concept of distributing a negative through a parentheses group can be challenging for students, so this lesson focuses on students understanding that when an expression is subtracted, every term in the expression is subtracted, not just the first term.

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Anchor Problems

25-30 minutes


Problem 1

Consider the numerical expression: $${12-(3+4)}$$

The expression is rewritten so it does not include parentheses. Which expression will give the same value as the original expression? Explain your reasoning for each one.

$${12-3+4}$$                  $${12-3-4}$$             

Guiding Questions

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Student Response

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Problem 2

Subtract: $${(4x+9y-4)-(7x+10)}$$

Guiding Questions

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Student Response

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Problem 3

Match each subtraction problem on the left with the equivalent simplified expression on the right.

A.  $$5x-(3x+1)$$

1.  $$-8x-1$$

B.   $$5x-(-3x-1)$$

2.  $$-2x+1$$

C.   $$-5x-(3x+1)$$

3.  $$2x-1$$

D.   $$-5x-(-3x-1)$$

4.  $$8x+1$$

Guiding Questions

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Student Response

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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


Two expressions are given below. 

Expression A:      $${5q-r}$$

Expression B:      $${ -2q+3r-4}$$

a.   Write a simplified expression that represents A + B.

b.   Write a simplified expression that represents A - B.

Student Response

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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 error analysis problems of subtraction problems where not every term in the parentheses was subtracted.
  • Include procedural problems where students add and subtract expressions—can be more than two expressions or addition and subtraction combined. (Do not include problems where a multiple of an expression is subtracted, such as $${5x - 2(3x - 8)}$$. This will come in Lesson 7.)
  • Challenge: Expression $$A$$ is given by $$3-x$$. Expression $$B$$ is given by $$-x-3$$. Write a simplified expression that represents $$-A-B-B-A$$.

Next

Simplify expressions by combining like terms and using the distributive property and properties of operations (Part 1).

Lesson 7
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Lesson Map

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

Topic A: Evaluating Numerical and Algebraic Expressions

Topic B: Generating Equivalent Expressions

Topic C: Solving Multi-Step Problems using Expressions

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