CALCULATING THE PERIMETER AND AREA OF A RECTANGLE.


Each pupil chooses 2 sheets of origami paper covered with a grid of squares.


A discussion question: What shape is the grid sheet? Check with your measurement tool. Explain.

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.


Answer:The grid paper has the shape of a square.


A discussion question: What is the length of the perimeter of each grid sheet? How can you calculate the length?


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.

The perimeter is 48 cm. 48=12+12+12+12


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.


Answer 3: The length of each side of the small square is 1 cm. The area of each small square is 1 sq.cm.


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?


Answer: The number of small squares on the grid sheet is 144. (12×12). The area of the grid sheet is 144 square cm.


Folding instructions: Cut your grid sheet into 4 rectangles with the following measurements. 3×12, 4×9, 6×6. All measurements are cm.

Keep the remaining part of the grid sheet.


A discussion question: What is the perimeter measurement of each rectangle? Explain.

Point out that the square is also a rectangle. This allows calling the three shapes with one name for the group.


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.

1. 2 x 3+2 x 12
2. 4 x 6
3. 2 x 4+ 2 x 9


An activity: Join the 3 rectangles together to form a new polygon shape.


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.

This activity will help the pupils in finding ways to measure perimeters of non regular or non rectangular shapes.


A discussion question:What is the area measurement of each rectangle? How did you find it? Explain.


Answer 1: Check the areas by multiplying the lenghts of adjacent sides of each rectangle.

Point out to the pupils that there are four possibilities in each rectangle for choosing a pair of adjacent sides


Answer 2: Each rectangle has an area measurement of 36 square cm.


An activity: Join the 3 rectangles together to form a new polygon shape.


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.

The rectangles should be joined at sides and not at the vertices.


Folding instructions: Turn over the 3 rectangles.


Folding instructions: Fold each rectangle as shown.


A discussion question: What are the area measurements of the three polygons after the folding.

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.


Answer: The area measurement of each shape is 18 square cm.


Folding instructions: Fold the vertices of the triangular shape as shown.


Folding instructions: Join the three shapes to obtain a puppy on a fence.


Final activity: What is the area measurement of your remaining shape?Can you suggest different ways to find the area measurement?

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