Curriculum / Math / 3rd Grade / Unit 5: Shapes and Their Perimeter / Lesson 9
Math
Unit 5
3rd Grade
Lesson 9 of 16
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Find perimeter of regular polygons and of rectangles when some side lengths are not given.
The core standards covered in this lesson
3.MD.D.8 — Solve real world and mathematical problems involving perimeters of polygons, including finding the perimeter given the side lengths, finding an unknown side length, and exhibiting rectangles with the same perimeter and different areas or with the same area and different perimeters.
The foundational standards covered in this lesson
3.OA.D.8 — Solve two-step word problems using the four operations. Represent these problems using equations with a letter standing for the unknown quantity. Assess the reasonableness of answers using mental computation and estimation strategies including rounding. This standard is limited to problems posed with whole numbers and having whole-number answers; students should know how to perform operations in the conventional order when there are no parentheses to specify a particular order (Order of Operations).
The essential concepts students need to demonstrate or understand to achieve the lesson objective
Suggestions for teachers to help them teach this lesson
“Perimeter problems for rectangles and parallelograms often give only the lengths of two adjacent sides or only show numbers for these sides in a drawing of the shape. The common error is to add just these two numbers. Having students first label the lengths of the other two sides as a reminder is helpful” (MD Progression, p. 16).
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Tasks designed to teach criteria for success of the lesson, and guidance to help draw out student understanding
Chris is replacing the fence around his rectangular backyard. Chris’s drawing of the backyard is shown below. Chris measured two of the side lengths and labeled them in his drawing.
How much fencing does he need to buy?
Grade 3, Unit 6, Lesson 9 (2017-2018) is made available by Achievement First as a part of their Open Source web portal under a CC BY 4.0 license. Copyright © 1999-2017 Achievement First. Accessed Feb. 11, 2019, 9:53 a.m..
The following shape is a regular polygon.
What is the perimeter, in centimeters, of the shape?
Problem Set
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A task that represents the peak thinking of the lesson - mastery will indicate whether or not objective was achieved
Find the perimeter of the rectangle below.
Find the perimeter of the regular hexagon below.
Which of the shapes above has a greater perimeter? How much greater? Show or explain your work.
An example response to the Target Task at the level of detail expected of the students.
The Extra Practice Problems can be used as additional practice for homework, during an intervention block, etc. Daily Word Problems and Fluency Activities are aligned to the content of the unit but not necessarily to the lesson objective, therefore feel free to use them anytime during your school day.
Extra Practice Problems
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Lesson 8
Lesson 10
Topic A: Attributes of Two-Dimensional Shapes
Compare and classify polygons.
3.G.A.1
Compare and classify quadrilaterals.
Draw shapes with specified attributes.
Reason about composing and decomposing polygons using tangrams.
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Topic B: Understanding Perimeter
Understand perimeter to be the boundary around a two-dimensional shape. Compare perimeters of various polygons using concrete non-standard units.
3.MD.D.8
Find perimeter of polygons whose sides are marked with unit length marks by counting the unit lengths.
Find perimeter of shapes with all side lengths labeled.
Find perimeter by measuring side lengths in whole number units.
Solve word problems involving finding perimeter given the side lengths.
Find side lengths of regular polygons and of rectangles when given perimeter and other side lengths.
Solve more complex word problems involving perimeter, such as finding a missing side length given perimeter and other side lengths.
Topic C: Distinguishing Between Area and Perimeter
Find rectangles with the same area and different perimeters.
Find rectangles with the same perimeter and different areas.
Solve a variety of word problems involving area and perimeter.
Reason about composing and decomposing polygons with various areas and perimeters using tetrominoes.
3.G.A.1 3.MD.D.8
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