Khan Academy Wiki

The Perimeter 2 exercise appears under the 3rd grade (U.S.) Math Mission, 4th grade (U.S.) Math Mission. This exercise has several applications of perimeter.

Types of Problems[]

There are three types of problems in this exercise:

  1. Find the missing length: This problem has a polygon drawn with an unknown side, and the total perimeter. The user is asked to find the missing length and write it in the space provided.
    P2-1

    Find the missing length

  2. Solve the problem with perimeter: This problem has a shape and perimeter like question about the shape. Users are asked to find the correct answer to the problem and write it in the space provided.
    P2-3

    Solve the problem with perimeter

  3. Identify expressions of perimeter: This problem has a polygon drawn and several numerical expressions below it. The user is asked to identify all the expressions that can be used to correctly find the perimeter of the shape.
    P2-4

    Identify expressions of perimeter

Strategies[]

Knowing that perimeter is the sum of the lengths of all sides of a polygon is the only knowledge needed to do this problem correctly. Careful reading is needed on some problems.

  1. Perimeter is the sum of the lengths of all sides of a polygon.
  2. The numbers on this exercise are fairly small so it can be faster to perform the arithmetic mentally if possible.
  3. on the Solve the problem with perimeter problem it is important to read carefully. Sometimes more than one "copy" of the perimeter is needed to get the correct answer to the problem.
  4. On the Identify expressions of perimeter each total can be found and then the correct ones should be selected. Typically perimeter is the sum of a number of copies of a side length, but can be a multiplication expression if some sides are congruent.

Real-life Applications[]

  1. Perimeter is used for building a swimming pool. The owner of the pool wants to maximize the area within constraints of property and minimize the amount of digging and concrete, etc. that goes into the project. Yet the perimeter also defines length that is used for swimming races.
  2. Area and perimeter are used in many jobs for architecture and interior design.