Multiply!

5 min

Narrative

This Warm-up prompts students to compare four expressions. It gives students a reason to use language precisely (MP6). It gives the teacher an opportunity to hear how students use terminology and talk about characteristics of the items in comparison to one another.

Launch

Arrange students in groups of 2–4. Display the expressions for all to see. Give students 1 minute of quiet think time, and ask them to indicate when they have noticed three images that go together and can explain why. Next, tell students to share their response with their group and then together find as many sets of three as they can.

Student Task

Which three go together? Why do they go together?

A

7.9x7.9x

B

7.9+x7.9 + x

C

7.9⋅(-10)7.9\boldcdot (\text- 10)

D

-79\text-79

Sample Response

Sample responses:

A, B, and C go together because:

  • Each expression contains the number 7.9.
  • Each expression has more than just a single number.

A, B, and D go together because:

  • None of the expressions have parentheses.

A, C, and D go together because:

  • None of the expressions has addition or a sum.
  • If x=-10x=\text-10, then the expressions would all be equivalent.

B, C, and D go together because:

  • If x=-86.9x=\text-86.9, then the expressions would all be equivalent.
  • None of the expressions are multiplying by a variable.

Synthesis

Invite each group to share one reason why a particular set of three go together. Record and display the responses for all to see. After each response, ask the class if they agree or disagree. Since there is no single correct answer to the question of which three go together, attend to students’ explanations, and ensure the reasons given are correct.

During the discussion, prompt students to explain the meaning of any terminology they use, such as “positive,” “negative,” “addition,” and “subtraction,” and to clarify their reasoning as needed. Consider asking:

  • “How do you know . . . ?”
  • “What do you mean by . . . ?”
  • “Can you say that in another way?”
Standards
Building On
  • 6.EE.2.b·Identify parts of an expression using mathematical terms (sum, term, product, factor, quotient, coefficient); view one or more parts of an expression as a single entity. <em>For example, describe the expression 2 (8 + 7) as a product of two factors; view (8 + 7) as both a single entity and a sum of two terms.</em>
  • 6.EE.A.2.b·Identify parts of an expression using mathematical terms (sum, term, product, factor, quotient, coefficient); view one or more parts of an expression as a single entity. <span>For example, describe the expression <span class="math">\(2 (8 + 7)\)</span> as a product of two factors; view <span class="math">\((8 + 7)\)</span> as both a single entity and a sum of two terms.</span>
Building Toward
  • 7.EE.B·Solve real-life and mathematical problems using numerical and algebraic expressions and equations.
  • 7.EE.B·Solve real-life and mathematical problems using numerical and algebraic expressions and equations.

20 min

10 min

10 min