Mathematics / Year 9 / Measurement and Geometry / Geometric reasoning

View on Australian Curriculum website Australian Curriculum, Assessment and Reporting Authority
Curriculum content descriptions

Solve problems using ratio and scale factors in similar figures (ACMMG221)

  • establishing the relationship between areas of similar figures and the ratio of corresponding sides (scale factor)
General capabilities
  • Literacy Literacy
  • Numeracy Numeracy
  • Critical and creative thinking Critical and creative thinking
ScOT terms

Ratios,  Scale (Proportions),  Similarity (Geometry)

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Year level 9-10
Resource type
Learning area Mathematics
Interactive resource

Exploring ratios and proportions

Explore ratios by comparing the dimensions of two rectangles. Choose a scale to enlarge the smaller shape and identify whether its sides are proportional to those of the larger rectangle. For example, a rectangle with sides in the ratio 4:5 has an equivalent ratio to a rectangle with sides in the ratio 12:15. Watch a video ...

Interactive resource

Trigonometry: measuring with triangles

Compare the shadows cast by a small stick and a larger object such as a column of a Greek building. Check the angles at which the shadows are cast and confirm whether the two objects create similar triangles. Use equivalent ratios to calculate the lengths of a triangle's sides: the height of an object or the length of a ...

Interactive resource

EagleCat: scale it

Explore changes in area when a shape is acted on by a scale factor. Examine changes in volume when an object is acted on by a scale factor. Analyse the changes using whole numbers.

Interactive resource

Measures: scaling up

Compare the areas of squares, rectangles and triangles before and after being scaled up (enlarged). Notice that 'similar shapes' in the mathematical sense have the same shape but different areas. Explore the relationship between side-length enlargement and area enlargement when scaling up shapes. This learning object is ...

Teacher resource

reSolve: Pythagoras' Theorem

This sequence of lessons challenges students to apply Pythagoras' Theorem to explore practical and historical real-world problems. In the first lesson students investigate the connection between their solutions and concepts of symmetry and algebra. In the second lesson, they explore technology reliant on mathematical concepts. ...

Interactive resource

HOTmaths: using a centre of enlargement

Investigate the effect of changing the scale factor on the enlargement of a quadrilateral and notice the effect on corresponding sides of a quadrilateral. Notice that the position of the centre of enlargement also affects the scale factor.

Interactive resource

Measures: similar shapes

Compare the sizes and angles of a range of triangles, squares and rectangles. Notice that 'similar shapes' in the mathematical sense have the same shape and possibly different sizes. Corresponding sides are in proportion, and corresponding angles are equal. Identify shapes that are similar and create shapes similar to given ...

Interactive resource

Measures: scaling down

Compare the areas of squares, rectangles and triangles before and after being scaled down (reduced). Notice that 'similar shapes' in the mathematical sense have the same shape but different areas. Explore the relationship between side-length reduction and area reduction when scaling down shapes. This learning object is ...

Interactive resource

Trigonometry: finding angles

Look at an explanation of the trigonometric ratios: sine, cosine and tangent. Adjust the angles of a right-angled triangle within a unit circle (radius of one unit). Set the cosine, sine and tangent values of angles from 0–90 degrees. Identify the angle for each of the values. This learning object is one in a series of ...

Interactive resource

In proportion: variables in ratios

Complete customer orders for a large hardware store by interpreting the ratios. Work in the gardening department to fill orders for liquid fertiliser (expressed as ratios). Examine the equations suggested to you by your colleagues. Choose and solve the correct equation to complete each order. This learning object is the ...

Interactive Resource

Renovate, Calculate!

A student resource that explores the use of mathematics in the trades. Highly interactive investigations into ratio, areas of special quadrilaterals and right-angled trigonometry.

Assessment resource

Vitality drinks: assessment

Assess your ability to make drinks from a menu to match customer orders. For example, calculate the volume of each juice type required when given the ratio of juices for a drink of a particular total volume. Watch an animation to determine the ratio of juices in a new recipe. Calculate the volume of each juice in the new ...

Interactive resource

In proportion: graphs of ratios, rates and scales

Complete customer orders for a large hardware store by interpreting ratios, rates and scales. Work in the manager's office and discover how ratios, rates and scales can be represented as graphs. Use the graphs to discover quantities for garden fertiliser ingredients, the cost of mulch, and for finding lengths of timber ...

Interactive resource

Measures: volumes

Compare the volumes of a range of rectangular prisms when scaling up (enlarging) side lengths by different ratios. Notice that the rectangular prisms are not similar in the mathematical sense, but it is possible to predict the effect on the volume produced by the scaling of the sides. Identify and describe the relationship ...

Teacher resource

MoneySmart: How can we obtain more money?

This is a year 9 mathematics unit of work about making money. Intended to take about ten hours, the unit consists of six sets of student tasks supported by teacher notes. Tasks include investigating part-time work; surveying class members about the hours they work; using a spreadsheet; calculating earnings and interest; ...


Australia's population: countries of birth - dataset

The dataset provides statistics about the estimated resident population, median age and sex ratio by countries of birth for the latest year of available data. It is periodically updated by the Australian Bureau of Statistics (ABS). The dataset is in MS Excel format.


International migration database

This is a web resource consisting of a database showing the movement of the ‘migrant’ population, generally the foreign-born population, to and from each of the OECD countries. Data tables can be customised with options to view by country of origin of the migrants, or by the variable to be displayed, for example, asylum ...

Teacher resource

reSolve: Mechanical Linkages: Similar Triangles

This sequence of lessons explores the geometry of similar triangles using two real world objects: ironing boards and pantographs. In the first lesson, students investigate different ironing board leg lengths and pivot positions using similar and congruent triangles. In the second lesson, they use their knowledge of parallelogram ...

Interactive resource

Measures: scaling surface area

Compare the surface area of cubes and rectangular prisms before and after being scaled up (enlarged) or scaled down (reduced). Notice that 'similar shapes' in the mathematical sense have the same shape but different surface areas. Explore the relationship between side length and surface area when scaling solids. This learning ...

Interactive resource

Exploring powers of 10

Examine a table of numbers expressed using base 10 exponents. Look at their equivalents expressed in other numeric formats such as expanded values and fractional exponents. Arrange the numbers within each group in descending order of magnitude. Use a scalable viewer to examine a scene within a valley in Canada. Look at ...