## Basic Math and Pre-Algebra

**PART 3. The Shape of the World**

**CHAPTER 14. Quadrilaterals and Other Polygons**

**Perimeter of Quadrilaterals**

It’s easy to calculate the perimeter of quadrilaterals. Just as with triangles, you simply add up the lengths of the sides. Most figures don’t even have a special formula for perimeter.

For a rectangle, you see the formula P = 2L + 2W. Because the opposite sides are the same length, you have two of the lengths and two of the widths. For a square or a rhombus, that becomes P = 4s. All the sides are the same length, and you have four of them.

Let’s look at a story problem using perimeter.

Suppose Marianna wants to build a fence around her vegetable garden. If the garden is a rectangle 30 feet long and 15 feet wide, and fencing costs $1.25 per foot, how much will it cost to fence the garden?

The perimeter of a rectangle is P = 2L + 2W, so she will need (2 x 30) + (2 x 15) = 60 + 30, or 90 feet of fencing. 90 feet of fencing at $1.25 per foot will cost 90 x 1.25 = $112.50. Marianna’s fence will cost $112.50.