Grade 3 Geometry: Perimeter

Worked examples

Real problems from the practice worksheets, solved one step at a time.

1. Example 1

   A square has sides that are 4 ft long. What is its perimeter in feet?

   1. Perimeter is the distance all the way around the square. Add the four sides.
   2. Perimeter = 4 + 4 + 4 + 4 = 2 × (4 + 4) = 16 feet.

   Answer: 16

2. Example 2

   A quadrilateral has a perimeter of 38 in. 3 of its sides are 9 in, 9 in, and 8 in. How long is the last side, in inches?

   1. All the sides add up to the perimeter. Add the sides you know: 9 + 9 + 8 = 26.
   2. Last side = 38 − 26 = 12 inches.

   Answer: 12

3. Example 3

   A rectangle has a perimeter of 18 ft. Its length is 5 ft. What is its width, in feet?

   1. The perimeter is 2 lengths + 2 widths, so one length + one width is half of it: 18 ÷ 2 = 9.
   2. Width = 9 − 5 = 4 feet.

   Answer: 4