New
New
Year 5

# Choose an efficient way to decompose a compound shape to calculate the area

I can choose the most effective way to decompose a shape into rectangles in order to calculate the area.

New
New
Year 5

# Choose an efficient way to decompose a compound shape to calculate the area

I can choose the most effective way to decompose a shape into rectangles in order to calculate the area.

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## Lesson details

### Key learning points

1. Different methods for finding the area of compound rectilinear shapes will work in different situations.
2. Compound rectilinear shapes can be split in different ways in order to calculate the area.
3. Compare different methods to decompose shapes and decide which is the most efficient.

### Common misconception

That a shape always has to be split into smaller shapes in order to calculate the area.

Show different ways to calculate area using the same shape. It can be split in different ways, completed and an area subtracted or a part cut and fitted into a gap.

### Keywords

• Compound - A compound shape is made up of two or more shapes.

### Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Starter quiz

### 6 Questions

Q1.
x 9 = 63
Q2.
This compound shape is made from a large square and a smaller rectangle. Which multiplication facts could you use to help find the total area of this shape?
7 x 3
5 x 7
Q3.
Which of these is NOT a compound rectilinear shape?
Correct Answer: An image in a quiz
Q4.
Which of the statements are true?
c is 10 cm long
Correct answer: d is equal to side f subtract 6
Correct answer: Side e plus side c is equal to 16 cm
d is 4 cm long
Q5.
What is the total area of this compound shape?
Correct Answer: 74 cm², 74 cm², 74cm2, 74 cm2, 74
Q6.
What is the total area?
Correct Answer: 61 cm², 61cm², 61cm2, 61 cm2, 61

## Exit quiz

### 6 Questions

Q1.
A shape is made up of two or more shapes. Complete the statement.
Q2.
True or False. This is the only way to split the compound shape into two rectangles.
True
Q3.
What is the length of the missing side?
10 cm
12 cm
9 cm
Q4.
Match the image to the strategy.
16 cm² + 56 cm² = 27 cm²
24 cm² + 48 cm² = 72 cm²
Correct answer: 84 cm² - 12 cm² = 72 cm²
Q5.
Which calculation would you use to find the area of this shape in the way it has been split into rectangles?
Correct answer: 18 cm² + 6 cm² = 24 cm²
18 cm² - 6 cm² = 12 cm²
Correct answer: 6 cm² + 18 cm² = 24 cm²
Q6.
Which pair of multiplications will help calculate the area of this compound rectilinear shape?
3 x 12 and 5 x 9
Correct answer: 3 x 12 and 5 x 6
5 x 9 and 3 x 12
Correct answer: 5 x 9 and 3 x 7