# Stage 3 – perimeter

## Strategy

Students can:

• use a ruler and other measuring devices to measure lengths in metres, centimetres and millimetres
• record lengths in decimal notation

## Activities to support the strategy

### Activity 1

1. Students in stages 1 and 2 can use informal units to measure around various shapes

2. Discuss the word perimeter. ‘Perimeter’ is derived from the Greek words that mean to measure around the outside: peri meaning ‘around’ and metron meaning ‘measure’.

3. Students are given a worksheet with a variety of drawings of squares, rectangles and triangles. Calculate and record the perimeter of each shape. View/print (PDF 687.4KB)

4. Discuss the strategies students used by asking these questions.

• How did you calculate the perimeter of each shape?
• Is there an easy way to calculate the perimeter of squares and rectangles?
• Is there an easy way to calculate the perimeter of different types of triangles?

### Activity 2

Students measure the perimeter of objects in their surroundings, such as books, desks, windows, classroom floor, oval or playground. Students choose an appropriate measuring device and measurement unit, justifying which measuring tool would be most suitable to measure different objects, e.g. a trundle wheel for larger areas or ruler or tape measure for tables.

Discuss and compare the strategies students used to calculate the perimeter, then students write a report to explain their strategies.

Where students had different perimeters recorded for the same object, determine the difference and discuss where the measurement error may have occurred.

### Activity 3

Using centicubes, students construct squares and rectangles of given perimeters, e.g. 24 cm.

Discuss:

• How many different rectangles can you make with a perimeter of 24 cm? Students make a list of the dimensions of each.
• Can you make different squares with a perimeter of 24 cm? Students give reasons to support their answer.
• Can you change one of the rectangles to make a different polygon but with the same perimeter?

## References

### Australian curriculum

ACMMG109: Calculate the perimeters of rectangles using familiar metric units and use the term 'dimensions' to describe the 'lengths' and 'widths' of rectangles

### NSW syllabus

MA3-9MG: Selects and uses the appropriate unit and device to measure lengths and distances, calculates perimeters, and converts between units of length.

## Teacher resources

• Round the outside – Students can calculate the perimeter of different shapes, choose the appropriate measuring device and make different shapes from given perimeters.