Calculate missing dimensions in rectangles and compound rectilinear shapes | Maths

Starter quiz

______ x 7 = 56

'8' ✓
96 = ______ x 8

'12' ✓
Which of these compound rectilinear shapes have a total area of 60 m²?

a

b ✓
Which calculation would you use to calculate the area with the information you have been given?

72 cm² − 10 cm² = 62 cm²

42 cm² + 20 cm² = 62cm² ✓

48 cm² + 14 cm² = 62 cm²
Jun worked out the area of a compound shape. Which of these shapes was he calculating the area of?
What is the area of the grey path around the pond?

'46m²' ✓

Exit quiz

What is the missing dimension

'4 cm' ✓
What is the missing dimension?

'7 cm' ✓
What is the missing dimension?

'23 cm' ✓
The area of this compound shape is 116 cm². What is the missing dimension?

6 cm

7 cm ✓

8 cm

5 cm
Here is a shape made from three identical rectangles. The area of the shape is 180 cm². What are the missing dimensions?

12 cm and 6 cm

11 cm and 5 cm

12 cm and 5 cm ✓

11 cm and 6 cm
The larger blue rectangles are double the area of the smaller red rectangles. Calculate the area of a small red rectangle.

'50 cm²' ✓

Worksheet

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Presentation

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Video

Lesson Details

Key learning points

Division is used to calculate a missing dimension when the area and the other dimension are known.
Inverse operations are used to calculate missing dimensions when areas are known.
Compare different methods to decompose shapes and decide which is the most efficient.

Common misconception

Applying known facts and strategies to solve problems involving division. Being able to break down a problem into steps when it comes to compound shapes.

Provide opportunities to discuss approaches and highlight the efficient strategies and approaches. Acknowledge that there is more than one way to solve a problem whilst focusing on efficient and effective strategies.

Keywords

Compound - A compound shape is made up of two or more shapes.
Dimension - A dimension is a measurement of length in one direction. Width and height are examples of the dimensions of 2D shapes.