How to Compute Perimeter and Circumference « Free Lessons

How to Compute Perimeter and Circumference

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