4.10 Compare sizes

Mathematics

More geometry, data handling and probability

Educator section

Memorandum

(b) 2 twice more; 3 times more;

5 times more than first rectangle

(c) 16 times

4.2.1 – 4.2.4 Check learner’s effort.

Leaner section

Content

Activity: compare sizes [lo 4.2, lo 3.8]

3. LET US COMPARE SIZES!

The following rectangle has been enlarged first two times, then three times and then five times.

All the rectangles have the same ratio for length to breadth: 3:2.

a) Look again at the rectangles above. Suppose that each block is 1 cm by 1 cm. Complete the table.

b) What happens to the perimeter each time the rectangle is enlarged?

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c) How many times larger is the area if the rectangle is enlarged four times?

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4.1 Did you know?

The ratio to scale is always written in a specific way:

The first number refers to the drawing/plan.

The second number refers to reality.

A scale of 1:5 means that the length is 5 times smaller than in reality.

A scale of 5:1 means that the length is 5 times bigger than in reality.

4.2.1 Use the graph paper and enlarge the sketch on a scale of 4:1.

4.2.2 Enlarge this drawing on a scale of 1:2.

4.2.3 Reduce this sketch on a scale of 2:1.

4.2.4 BRAINTEASER!

• Can you enlarge this drawing and re-draw it?

Assessment

Learning Outcome 3: The learner will be able to describe and represent characteristics and relationships between two-dimensional shapes and three-dimensional objects in a variety of orientations and positions.

Assessment Standard 3.8: We know this when the learner locates positions on co-ordinate systems (ordered grids) and maps

Learning Outcome 4: The learner will be able to use appropriate measuring units, instruments and formulae in a variety of contexts.

Assessment Standard 4.2: We know this when the learner solves problems.