Complex shapes

Work out the area of this shape

Calculating area

Calculating perimeter

The perimeter is the length around

the edge of a shape.

How do you calculate the perimeter

of a shape?

Perimeter

**Perimeter**

and

Area

and

Area

Work out the perimeter of the sheet of paper you are using.

You can work with a partner

if you like!

Calculate the perimeter of this shape.

75 cm

1.75 metres

Units need to be the same

BEFORE working out perimeter.

75 cm = 0.75 m

The shape is a rectangle so

opposite sides are equal in length

Perimeter = 0.75 +1.75 + 0.75

+ 1.75

= 5 m

How would you work out the perimeter of this shape?

2 cm

20cm

5cm

3cm

15cm

5cm

You might want to copy the diagram!

Add up all the lengths!

Perimeter = 20 + 5 +15 + 3 +

5 + 2

= 50 cm

Work out the perimeter of a square that has sides measuring 6cm.

HINT: Draw a sketch first

Extra challenge:

The perimeter of a square is 32 metres. How long are the sides of the square?

Since the shape is a square, all the

sides will be 6 cm long.

Perimeter = 6 + 6 + 6 + 6

= 24 cm

AREA

The area is the amount of surface

(or space) covered by a flat shape.

Area is always measured in

square units eg,

square centimetres , cm

4 metres

8 metres

We can calculate the area of the above shape

by multiplying the length by the width

Area = 8 x 4 = 32 m

13 m

2 m

Extra challenge:

Work out the area of a rectangle with

sides 34 mm and 50 mm

Area = length x width

= 2 x 13

= 26 m

Extra challenge

Area = 50 x 34 = 1700 mm

1.3m

75cm

Extra:

Give possible dimensions for a rectangle with

area 80mm

Need to make units the

same first.

75 cm = 0.75 m

Area = 0.75 x 1.3

= 0.975 m

Extra - 10mm x 8 mm, 20mm x 4 mm etc

3cm

5cm

15cm

6cm

Calculate the area of this shape

Possible solution

Split the shape into 2 rectangles:

15cm

6cm

3cm

5cm

Area of bigger rectangle = 6 x 15 = 90 cm

Area of smaller rectangle = 3 x 5 = 15 cm

Total area = 90 + 15 = 105 cm

Practical examples:

Discuss with your partner

times when it would be

useful to know the area and

perimeter of a shape.

Can you come up an

example of each?

2

2

2

2

2

2

2

2

2

2

HINT: Be careful with the units

Extra:

Perimeter = 32 cm

Each side must be 32/4 = 8 cm long

CHECK: 8 + 8 + 8 + 8 = 32 cm