WALT: Calculate the area and perimeter of rectilinear shapes

The formula you need to know and remember are:

𝑝 = 2𝑙 + 2𝑤 (𝑖𝑓 𝑡ℎ𝑒 𝑠ℎ𝑎𝑝𝑒 𝑖𝑠 𝑟𝑒𝑔𝑢𝑙𝑎𝑟!)

a = l x w

• 2L + 2W if you have a regular shape with all sides labelled

• Calculate any missing lengths

• Add all the lengths together What does rectilinear mean?

To calculate the area of this shape, what formula would I need to use?

To calculate the perimeter of this shape, what formula would I need to use?

Will your answers be the same?

Remember: unit of measure!

To calculate the area of this shape, what formula would I need to use?

a = l x wa = 3 x 4

a = 12cm2

To calculate the perimeter of this shape, what formula would I need to use?

P= 2l x 2wp = (3x2) + (4x2)

P = 6 + 8P = 14cm

No – in this example, the area and the perimeter are not the same.

Calculate the area and perimeter of these shapes.

Do any of them have the same area and perimeter?

Shape A

Shape B

Shape C

Shape D

Shape E

Shape A

Shape C

Shape B

Shape D

Shape E

Shape Area Perimeter

A 6 x 3 = 18cm2 (6x2) + (3x2) = 18cm

B 6 x 6 = 36cm2 6 x 4 = 24cmThis is a square so all the sides are

of equal length.

C 9 x 5 = 45cm2 (9x2) + (5x2) = 28cm

D 8 x 2 = 16cm2 (8x2) + (2x2) = 20cm

E 7 x 8 = 56cm2 (7x2) + (8x2) = 30cm

Calculate the area and perimeter of this shape.Remember to use the same strategy as when we found the area of a compound shape on Monday 23rd March 2020 (activity 1).

Calculate the area and perimeter of this shape.

Area:Split the compound shape into two regular shapes. • To calculate the area of part A, multiply 2 x 2 = 4cm2

• To calculate the area of part B, multiply 5 x 3 = 15cm2

• Add the total of the two parts together:15cm2 + 4cm2 = 19cm2

Part A

Part B

Calculate the area and perimeter of this shape.

Perimeter:• Calculate any missing lengths• The green length is missing – use any parallel sides (shown in

pink) to find the missing length• I would need to subtract 2 from 5 to find the green side so…• 5 – 2 = 3

• Add all the sides together to find the perimeter:

5 + 5 + 2 + 2 + 3 + 3 = 20cm

Calculate the area and perimeter of this shape.Remember to use the same strategy as when we found the area of a compound shape on Monday 23rd March 2020 (activity 1).

CHALLENGE!Calculate the area and perimeter of this shape.

Calculate the missing value.Perimeter = 36cm

See the next two slides for bar modelling and how to work this out!

Calculate the missing value.Perimeter = 36cm

36

5 5

?

Calculate the missing valuePerimeter = 36cm

36

5 5 13 13

26

Calculate the missing value.Perimeter = 22cm

Use a bar model to solve this.

Calculate the missing value.Perimeter = 22cm

?

Calculate the missing valueArea = 40cm2

Remember to use the formula!If I know that…

a = L x w Then I also know that…

L = a ÷ wW = a ÷ L

40cm2 = 5 x ?

Now, use the inverse operation to calculate the answer…

40 ÷ 5 = 8cm2

So the missing value is 8cm2.

Calculate the missing valueArea = 65cm2

Remember to use the formula!

a = l x w

Now, please have a go at The White Rose activity to practise finding the area of compound

shapes!

You can find a PDF printable copy on the blog. There is also a screenshot of the activities on the two next two slides. The answers can be found in

slides 21-22.