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Grade 3: Calculating Area

Objectives:

Students will be able to:

  • Calculate area by counting “tiles”;
  • Calculate area by multiplying length times width; and
  • Use the appropriate unit of measure, e.g., square inches, square meters, etc.

Time Required: 30–40 minutes

Note: Lesson assumes students have already been taught perimeter.

Materials:

Directions:

  1. Prior to the lesson, draw a  5" x 6" rectangle on a piece of 1" grid paper.
  2. Show the class the 5" x 6" rectangle. Indicate that the drawing is a floor plan for a storage unit at the school with a scale of 1 inch = 1 foot. First, ask class to find the perimeter of the storage unit (5' + 6' + 5' + 6' = 22' or 2(5' + 6') = 22'). Review concept of perimeter as necessary. Make sure that students understand that the correct unit of measure for the perimeter of the storage area is feet.
  3. Tell the class that the floor of the unit will be covered in one-foot tiles. Ask how many tiles it will take to cover the floor of the unit. Show that it will take 30 tile squares to cover the floor by counting the number of squares on the grid paper within the perimeter of the storage unit.
  4. Ask the class if the drawing reminds them of something they saw when they learned multiplication (an array). Point out that the plan of the storage unit can be seen as a 5 x 6 array. Ask if it is necessary to count the squares to find the total number of squares (no, simply multiply 5 x 6 = 30). Indicate that the proper unit of measure for the area of the storage unit’s floor is 30 square feet and that the proper unit of measure for area in general is square units.
  5. Distribute grid paper to students. Ask them to draw a rectangle with an area of 24 square inches. Circulate and ensure that the drawings represent 24 square inches. Ask students for the dimensions of their rectangles. Ask if students who drew a 4" x 6" rectangle and students who drew a  3" x 8" rectangle can both be correct and point out that since the product of 4 and 6 as well as 3 and 8 is 24 (or 1" x 24" or 2" x 12"), they are all correct. Indicate that although these rectangles have the same area, the perimeters are different.
  6. Distribute Worksheet 3.1 to class. Circulate while students are working.
  7. Review answers with class.

Mini-Poster: This colorful mini-poster provides a visual representation of the concepts addressed in all three lessons, and can be used by the teacher to illustrate points during each lesson for each grade level. After the lesson, the poster provides students with a visual reminder of the key measurement concepts taught.

Family Page: Distribute the family page for a fun take-home activity that also reinforces measurements skills at home.

Extension: Challenge students to come up with their own zany food-and-animal hybrid. Encourage them to sketch and measure their creation, and to also describe it. Click here to view a description of the fun Foodimal characters featured in these materials.

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