Lesson plan

9. Candy Costs: Solve a problem by comparing across more than two number lines (A)

teaches Common Core State Standards CCSS.Math.Content.7.NS.A.3 http://corestandards.org/Math/Content/7/NS/A/3
teaches Common Core State Standards CCSS.Math.Content.7.RP.A.1 http://corestandards.org/Math/Content/7/RP/A/1
teaches Common Core State Standards CCSS.Math.Content.7.RP.A.2b http://corestandards.org/Math/Content/7/RP/A/2/b
teaches Common Core State Standards CCSS.Math.Practice.MP1 http://corestandards.org/Math/Practice/MP1
teaches Common Core State Standards CCSS.Math.Practice.MP3 http://corestandards.org/Math/Practice/MP3
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Lesson Objective: Apply knowledge of unit rates and use multiple number lines to compare the costs across three items.

Students are typically asked to work with two rates. In this application problem, students compare three pairs of quantities that vary in different ways. Understanding how the parallel number lines show the relationships precedes understanding how the relationships will be shown with equations and graphs in Unit 2.

Key Concept students will use:

  • Quantities in a proportional relationship change together in the same way.

Skills students will use:

  • Using double number lines to explore proportional relationships between unlike units.

Students engage in Mathematical Practices 1 and 3. They must make sense of the problem, recognizing that the most obvious-seeming answer is not necessarily correct. They also must construct a viable argument for why Tiny-Tarts are the most cost-effective candy to buy.

Key vocabulary:

  • double number line

  • per

  • proportional relationship

  • rate

  • unit rate