Lesson plan

# 3. Duct Tape Bracelets: Apply understanding of proportional relationships and unit rates (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.2a http://corestandards.org/Math/Content/7/RP/A/2/a
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 understanding of both between and within relationships with like units.

In this lesson, students adjust dimensions to create different sizes of bracelets. They may work with the between relationship as they adjust the lengths based on the relationship they notice in the widths. Alternatively, they may figure out the lengths by noticing that the given dimensions show a length that is 9 times the width. This is an informal introduction to scaling.

Students engage in Mathematical Practices 1 and 3. They must make sense of the task because no clear entry point is given. Doing so requires them to use proportional reasoning. They also critique Diego’s reasoning when Diego claims that adding the same amount to both the length and width of a bracelet will maintain the proportional relationship.

Key vocabulary:

• proportional relationship

• unit rate