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.

 

Summary:

This standard explores the concept of perimeter as being the distance around the outside of a particular object, as well as determine unknown side lengths when given. Students will understand the difference between perimeter and area; perimeter does not determine area and area does not determine perimeter. Students will master the ability to calculate the perimeter of an object by measuring all the sides of an object and adding those measurements together.

Understanding the Standard:

  • In the beginning, have students write the measurement above each side and then write an addition equation for calculation.
  • Relate perimeter to real-life situations such as putting fence around an object or buying materials for a picture frame. The more ways students can see the application of this skill, the more ownership they will take in learning it.
  • Students should have the opportunity to measure a variety of objects and then calculate the perimeter.
  • Provide opportunities to find the side lengths of rectangles given only the perimeter and one side length, as well as rectangles with the same perimeter and different area, or rectangles with the same area and different perimeters.
  • The use of manipulative and technologies will help with students’ understanding.

Questions to Focus Instruction:

  • Can students articulate that perimeter is the distance around the outside of an object?
  • Can students cite examples of how the calculation of perimeter is important to real-life situations?
  • Are students able to find the length of an unknown side if the other side lengths and total perimeter is known?
  • Can students find the side-length of a rectangle if only one side-length and the perimeter are given?
  • Can students construct rectangles with the same area and different perimeter?
  • Can students construct rectangles with the same perimeter and different area?

Skills

Prior to: Students can add to find the perimeter of an object when the lengths of the sides are given.

At Grade Level:
Students have a strong understanding of the difference between area and perimeter, and can solve word problems involving perimeter. Students are able to make the connection between perimeter and real-life situations. Students can measure and calculate the perimeter of a variety of objects.