Area of rectangles for a mixed ability maths class

Finding the area of a rectangle is such a key skill in mathematics as it leads on to many other aspects of shape, number, algebra and even handling data.  In this blog I’ll take you through how I teach the area of rectangles for a mixed ability maths class in Year 7.

Difference between perimeter and area

Area of rectangles for a mixed ability maths class

A common misconception for Year 7s is to confuse the area of a rectangle with its perimeter.  The starter addresses this by challenging students to find the perimeter of a star, regular octagon and pentagon and hexagon.

Students are typically able to find the perimeter as a product of the number of sides and side length for the three regular shapes.  Less able students may find the perimeter by long addition.  Some forget to find the two missing lengths in the blue hexagon and write its perimeter incorrectly as 40 cm.

Area of rectangles for a mixed ability maths class

Area of rectangles for a mixed ability maths class

To phase in the main part of the lesson I highlight the difference between perimeter and area.  I do this by counting the number of squares inside the rectangle.  The majority of Year 7s know this from primary school.

As we progress, I ask the students to sketch a rectangle on their mini-whiteboard (1 whiteboard per pair so they have to work together to aid peer support).  I pose two questions one for the lower and core ability and one for the most able.

Lower and Core Ability

“A rectangle has a fixed area of 24 cm2.  What could the dimensions be?”

Area of rectangles for a mixed ability maths class

More able

“A rectangle has a fixed perimeter of 36 cm.  What could the different areas be?”

Area of rectangles for a mixed ability maths class

Rather than asking students to repetitively find the area as a product of its two sides I challenge students to find a missing length when given its area or to find both the length and width when given area and perimeter.  See the table below.

LengthWidthAreaPerimeter
12 cm8 cm
9 mm12 mm
6 in30 in^2
15 m46 m
11 cm7 cm^2
25 m36 m^2

To add further challenge for the most able I pose similar questions with algebraic dimensions.

Find the missing dimensions for these rectangles.  All lengths are in cm.

LengthWidthAreaPerimeter
av
2x5r
55(c + 15)
2c + y10c + 2y
4ff^2 - 1
1820 - 2c - 4c^2

Ambitious?  Yes, especially for Year 7 students.  But it constantly surprises me how much students can understand when expectations are high.

Assessing progress and leading on to composite areas
Area of rectangles for a mixed ability maths class

To wrap up this lesson and lead into the next on compound areas the plenary challenges students to find the area of a composite rectilinear shape.  I remind some students to find the missing lengths.  Others need some help seeing the composite shape as the sum or difference of two rectangles.

Either way, by the end of the lesson students are much more confident to solve problems involving the area of a rectangle.

 

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes:

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Mr Mathematics Blog

Sharing an Amount to a Given Ratio

There are three common methods for sharing an amount to a given ratio.  Depending on the age group and ability range I am teaching I would choose one approach over the other two. The three methods are: Using fractions Unitary method Using a table In this blog I will demonstrate each of the three methods […]

Plotting Scatter Graphs and Understanding Correlation

To introduce plotting scatter graphs and understanding correlation I ask students to think about the relationships between different variables and to describe how they might be related. Here’s my starter activity which students discuss in pairs then present to me on mini-whiteboards. When the students have had time to discuss the matching pairs we talk […]

Plotting Quadratic Graphs on Cartesian Axes

In recent examiner reports it is noted how important it is for students to understand the properties of a parabola  when plotting quadratic graphs on Cartesian axes.  Students who have a secure understanding of parabolas can use them to correct miscalculated values in their table of results and are more likely to attain full marks […]