Mathematics, Measurement (includes Time), Operations (+, -, x, /, etc.)

Grade 5- 8

### Objective

Students learn how to compute perimeter and circumference.

### Directions

Discuss with students the following facts. Go over the sample problems as a class.

Facts to Know

Perimeter is the distance around all the edges of an object.
The distance around a property such as a house, lot, or a schoolyard is the perimeter of the property.
The following words usually indicate perimeter: border, walls, fence, edges, sides, or distance around.

**Perimeters of Rectangles**

The perimeter of a rectangle can be computed by any of the following ways:
adding up all four sides of the rectangle
adding the length and width and multiplying by 2
using the formula: P = (l + w) x 2 or P = 2(l + w)

(Note: P = perimeter, l = length, and w = width)

Compute the perimeter of this rectangle. The length is 3.5 centimeters and the width is 2.4 centimeters.

Add the 3.5 plus 2.4, which equals 5.9 centimeters.

Multiply by 2 to get the other two sides of the rectangle.

The total perimeter is 11.8 centimeters.

**Perimeters of Other Polygons**

Add the sides of each polygon to compute the perimeter.

6.3 cm + 6.3 cm + 4.5 cm = 17.1 cm 7.3 cm x 5 = 36.5 cm

Circumference of a Circle

The formula for determining the circumference of a circle is 2πr or πd. (To solve, multiply 2 times r (the radius) times π (equals to approximately 3.14) or multiply d (the diameter) times 3.14.

Multiply 5 times 2 times 3.14 or

5 x 2 x 3.14 = 31.4 m, so C = 31.4 meters

### Resources

- activity sheets (3 per student)
- pencils