Mensuration

ObjectivePerimeter and area of shapes made

from triangles and rectangles

Does anybody know what perimeter is?The perimeter of a shape is all the way around the shape.

3cm

3cm

3cm

3cm

Perimeter =3+3+3+3 = 12cm

Pick a starting point!

Don’t forget units!

On your white boards find the perimeter of

these shapes…

8cm

16cm

12cm

10m

10m

4m4m

28m

8m

10m

5m

2m

3m

8m

5m

51m

4mm

10mm

5mm

6mm

42mm

Does anybody know what area is?

Area is the amount of space inside a shape.

Area of a rectangle

length

width

Area of a rectangle = length x width

ExampleFind the area of this rectangle

5cm

3cm

Area = length x widthArea = 5cm x 3cmArea = 15cm²

Don’t forget the correct units!

On your white boards find the area of these

rectangles…

10cm6

cm

60cm²

2mm

12

mm

24mm²

23km

2k

m

46km²

2m8

2cm

1.64m² or 16400cm²

Area of a triangle

Length

Heig

ht

---------------------------------------------------------------

Area = length x height_____________ 2

ExampleFind the area of this triangle

5c

m

8cm

Area = length x height

_____________ 2

Area = 8cm x 5cm__________ 2

Area = 20cm²

On your white boards find the area of these

triangles…

10

m

10m

50m²

6m

9m

27m²

3km

5km

Perpendicular height

7.5km²

10m

m 8m

m

9mm

8m

m

36mm²

Could you find the area of this shape?

10cm

12

cm

5cm

6cm

30cm²

4cm

48cm²

Area = 30cm² + 48cm²Area = 78cm²

10m

14m

5m

Could you find the area of this shape?

50m²

4m5

m 10m²

Area = 50m² + 10m²Area = 60m²