Polygon Perimeters with Tantalizing Tangrams!
Students will be able to find the perimeter of various polygons by adding the sides or measuring with a ruler.
- Read to your students Spaghetti and Meatballs for All! A Mathematical Story by Marilyn Burns (a story about perimeter), The Warlord's Puzzle by Virginia Walton Pilegard (a story about Tangrams), or another picture book to get them thinking about the learning they are about to dive into.
Explicit Instruction/Teacher modeling(10 minutes)
- Have your students turn to a partner and explain what perimeter is. Call on a few students to share what their partner said.
- Write on the board a student-friendly definition of perimeter (the distance around a two-dimensional shape). Explain to your students that the perimeter of a shape can be found by adding up the length of each side.
- Show your students a picture of a tangram puzzle. Ask them to name the polygons (two-dimensional shapes with three or more straight sides) they see in the puzzle. As they name the polygons, draw an example of the shape on chart paper and review the definitions:
- A triangle is a polygon with three sides and three angles.
- A parallelogram is a quadrilateral where opposite sides are parallel and of equal length, and opposite angles are equal.
- A square is a quadrilateral with four equal sides and four right angles.
- Show them that other polygons can be made from the tangram pieces like rectangles and trapezoids and then add these to your chart paper as well.
- A rectangle is a quadrilateral that has two pairs of parallel sides and four right angles.
- A trapezoid is a quadrilateral with one pair of parallel sides.
Guided Practice(10 minutes)
- Label the triangle on the chart paper with three measurements. Ask your students to find the perimeter. (They can use paper, white boards, or mental math.) Explain that finding the perimeter was pretty straight forward because all of the sides were labeled.
- Label the length and width of the parallelogram. Ask your students to turn to a partner and explain how to find the perimeter of this shape. Call on a few students to share their thinking. Make sure students understand how to figure out the unlabeled lengths and that they are not only adding up the labeled sides.
- Label one side of the square. Ask your students to turn to a partner and explain how to find the perimeter of this shape. Call on a few students to share their thinking.
- Tell your students that for the next shape, a rectangle, you already know the perimeter is 20 inches. Ask them what other information they would need to find the dimensions of the rectangle. (They need to know at least one of the lengths.)
- Label one side of the rectangle as 6 inches. Show your students how you then know the opposite side is also 6 inches and that the other two sides together must equal 8 inches because 20 inches minus the two 6 inch sides is 8 inches. Half of 8 inches is 4 inches, so the other two sides are each 4 inches.
- Practice finding the perimeter or missing lengths of a few more shapes with your students.
Independent working time(25 minutes)
- Give your students the Polygon Perimeter Word Problems Practice worksheet to complete on their own.
- Assist students as needed.
- Give each student a set of tangrams and piece of paper so they can create a picture, creature, or design by tracing the shapes.
- Have your students use rulers to measure and label the lengths of each shape and then find the perimeter of each shape.
- Give students complex figures to find the perimeter or missing side lengths. You could also have them create complex figures using the tangram pieces and then find the perimeter.
- Preteach vocabulary and highlight lengths and shape names on the practice worksheet.
- Ask students to choose one of the problems from the Polygon Perimeter Word Problems worksheet to share with their partner.
- Have them peer review each other's work. Invite a few students to share how they solved the problem in front of the class.
Review and closing(5 minutes)
- Have students do a gallery walk to view other students tangram perimeter designs and instruct students to compliment their peers on their pictures.