Grade 3 Math TEKS 3.7B:Perimeter Calculation

Learning Target: I can find the missing side length of a polygon when given the perimeter and the other side lengths.​

Focuses On:

• Using a part/whole diagram to find the missing side length of a polygon given the perimeter
• Determining the missing side lengths of regular polygons
• Finding the missing side length in a word problem

Builds On:

2.9E:

Determine a solution to a problem involving length, including estimating lengths.

1.7D:

Describe a length to the nearest whole unit using a number and a unit.

Next Level:

4.5D:

Solve problems related to perimeter and area of rectangles where dimensions are whole numbers.

Read More:

This lesson is designed to support student understanding of the concept of perimeter and how it can be used to find the length of a missing side of a polygon.

The lesson begins by relating the concept of finding the missing side length to a part/whole diagram students are familiar with from addition and subtraction problems. The lesson continues as students find the side lengths of regular polygons given the perimeter, and concludes by challenging students to solve word problems involving perimeter.

This lesson should be completed after "Finding Perimeter." It building on the foundation needed for 4th grade where students will need to find the perimeter and area of rectangles.

Learning Target: I can find the perimeter of a composite figure when given the side lengths.

Focuses On:

• Finding the perimeter of composite figures
• Determining the sides of composite figures that are not used in the perimeter calculation
• Identifying the measurements of missing side lengths in composite figures to determine perimeter
• Comparing the perimeters of composite figures

Builds On:

2.9E:

Determine a solution to a problem involving length, including estimating lengths.

1.7D:

Describe a length to the nearest whole unit using a number and a unit.

Next Level:

4.5D:

Solve problems related to perimeter and area of rectangles where dimensions are whole numbers.

Read More:

This lesson is designed to support student understanding of the concept of perimeter and how it is determined in composite figures- focusing especially on the sides of a composite figure that should not be included when calculating perimeter.

The three instructional blocks focus on calculating perimeter, determining the unknown side and comparing perimeters .

The first instructional block outlines the concept of a composite figure and how finding its perimeter is different than finding the perimeter of a polygon. Students then practice finding the perimeter of composite figures.

The second instructional block has students determine the perimeter of composite figures. In order to do this, they will also need to determine side lengths when given one length of a regular polygon.

The third instructional block gives students the opportunity to compare the perimeters of composite shapes.

Visual models and supported expressions are intentionally built into the lesson to support conceptual understanding.

Learning Target: I can determine the perimeter of a polygon when given its side lengths.

Focuses On:

• Defining and explaining the procedure for finding perimeter
• Finding the perimeter of polygons such as rectangles, squares, and triangles when given needed side lengths
• Identifying shapes with common perimeters
• Determining mistakes made when finding perimeter

Builds On:

2.9E:

Determine a solution to a problem involving length, including estimating lengths.

1.7D:

Describe a length to the nearest whole unit using a number and a unit.

Next Level:

4.5D:

Solve problems related to perimeter and area of rectangles where dimensions are whole numbers.

Read More:

This lesson is designed to support student understanding of the concept of perimeter and how it is determined given various side lengths of squares, rectangles, triangles, and other polygons.

The three instructional blocks focus on calculating perimeter-models, comparing perimeter and calculating perimeter.

The first instructional block begins by defining perimeter and explaining how it can be found when given 1 side length on a square or 2 side lengths on a rectangle. Students practice finding the perimeter of the models in each problem.

The second instructional block has students determine the perimeter of various polygons in order to find polygons with the same perimeter. Students will have the opportunity to make the connection that polygons can look different but have the same perimeter.

The third instructional block has students calculating the perimeter of polygons, without the use of a model. Students are given the shape name and side lengths and are asked to determine the perimeter. Students are also asked to determine common mistakes in determining perimeter.

Visual models and supported expressions are intentionally built into the lesson to support conceptual understanding.