CALCULATING THE PERIMETER AND AREA OF A RECTANGLE.
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CALCULATING THE PERIMETER AND AREA OF A RECTANGLE.
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Each pupil chooses 2 sheets of origami paper covered with a grid of squares.
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A discussion question: What shape is the grid sheet? Check with your measurement tool. Explain.
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The pupils have already learnt about three properties of a square shape. 1. Four right angles. 2.all sides have the same length. 3.Opposite sides are parallel.
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Answer:The grid paper has the shape of a square.
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A discussion question: What is the length of the perimeter of each grid sheet? How can you calculate the length?
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Answer 1: On each side of the squared shape grid paper there are 12 small square shapes and the length of the perimeter of the sheet is 48 length units.
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The perimeter is 48 cm. 48=12+12+12+12
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Answer 2: The length of each side of the small square is 1 cm. The length of the side of the grid sheet is 12 cm. The perimeter of the grid sheet is 48 cm.
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Answer 3: The length of each side of the small square is 1 cm. The area of each small square is 1 sq.cm.
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A discussion question: How many small squares are there on each row? How many rows are there on the grid sheet? How many small squares are on the grid sheet?
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Answer: The number of small squares on the grid sheet is 144. (12×12). The area of the grid sheet is 144 square cm.
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Folding instructions: Cut your grid sheet into 4 rectangles with the following measurements. 3×12, 4×9, 6×6. All measurements are cm.
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Keep the remaining part of the grid sheet.
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A discussion question: What is the perimeter measurement of each rectangle? Explain.
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Point out that the square is also a rectangle. This allows calling the three shapes with one name for the group.
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Answer: The rectangle marked 1 has a perimeter length of 30 cm. The rectangle marked 2 has a perimeter length of 24 cm. The rectangle marked 3 has a perimeter length of 26 cm.
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1. 2 x 3+2 x 12
2. 4 x 6
3. 2 x 4+ 2 x 9
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An activity: Join the 3 rectangles together to form a new polygon shape.
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A group activity: Check the perimeters of the new polygons and discover which shape has the largest perimeter or the smallest perimeter. The polygons shown are only suggestions.
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This activity will help the pupils in finding ways to measure perimeters of non regular or non rectangular shapes.
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A discussion question:What is the area measurement of each rectangle? How did you find it? Explain.
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Answer 1: Check the areas by multiplying the lenghts of adjacent sides of each rectangle.
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Point out to the pupils that there are four possibilities in each rectangle for choosing a pair of adjacent sides
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Answer 2: Each rectangle has an area measurement of 36 square cm.
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An activity: Join the 3 rectangles together to form a new polygon shape.
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A group activity: Check the area of the new polygons and discover which shape has the largest area or the smallest area. The polygons shown are only suggestions. Explain.
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The rectangles should be joined at sides and not at the vertices.
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Folding instructions: Turn over the 3 rectangles.
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Folding instructions: Fold each rectangle as shown.
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A discussion question: What are the area measurements of the three polygons after the folding.
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Point out that the area measurements are half of the original area as the rectangles were folded in half. Investigate the perimeters of each polygon.
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Answer: The area measurement of each shape is 18 square cm.
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Folding instructions: Fold the vertices of the triangular shape as shown.
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Folding instructions: Join the three shapes to obtain a puppy on a fence.
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Final activity: What is the area measurement of your remaining shape?Can you suggest different ways to find the area measurement?
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It is possible to find the area measurement in several ways by splitting the hexagon in different ways. The hexagon is not regular and is also concave.
- Lesson Aims
- The pupil will learn the measurement units cm and square cm using the units to measure perimeter and area of shapes.
- The pupil will learn how to computate perimeter and area of a rectangle.
- Computing perimeter and area of composite shapes made from rectangles.
- Computing of areas of objects in the environment.
- Computing maximum areas of shapes with given perimeter.
- Name of Model
The puppy on the fence.
- Lesson Structure
According to curriculum.
- Lesson Content
Using square grid paper to cut polygons of 36 square cm area and investigating perimeters of these shapes.
- Materials
2 sheets of squared grid origami paper 12cm x 12cm
