## 2021 Oregon Math Guidance: 3.GM.D.8

**Cluster: 3.GM.D - Geometric measurement: recognize perimeter. **

## STANDARD: 3.GM.D.8

### Standards Statement (2021):

Solve problems involving authentic contexts for perimeters of polygons.

### Connections:

Preceding Pathway Content (2021) | Subsequent Pathway Content (2021) | Cross Domain Connections (2021) | Common Core (CCSS) (2010) |

3.GM.C.5 | 4.GM.B.6 | N/A | 3.MD.D.8 3.GM.D Crosswalk |

### Standards Guidance:

#### Clarifications

- Students should be given opportunities to develop a conceptual understanding of perimeter of all types of polygons including regular and irregular.
- Students should investigate perimeters of polygons with a focus on quadrilaterals.
- Students should be able to find the perimeter given the side lengths.
- Students should be able to find the unknown side length given the perimeter.

#### Terminology

- The focus of this learning objective should be on developing the conceptual understanding of perimeter, rather than on terminology.
- A polygon is a closed figure with at least three straight sides and angles; a polygon is regular only when all sides are equal and all angles are equal; and a polygon is irregular when all sides are not equal or all angles are not equal.

#### Teaching Strategies

- Finding the perimeter given the side lengths;
- Finding an unknown side length;
- Showing rectangles with the same perimeter and different area;
- Showing rectangles with the same area and different perimeters.
- Students should solve contextual, mathematical problems involving perimeter and area of rectangles.

#### Progressions

- 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 those two numbers. Having students first label the lengths of the other two sides as a reminder is helpful. Students then find unknown side lengths in more difficult “missing measurements” problems and other types of perimeter problems. (Please reference page 16 in the Progression document).

#### Examples

- I have eighteen 1-foot panels to build a raised garden bed. How many different ways can I put these eighteen panels together to build a rectangular raised garden bed? Which rectangle will have the greatest area?