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8.01 Measure and estimate length


Are you ready?

Do you know what a length is? It is a measure of how big something is. This lesson we will look at measuring some lengths and making estimates on lengths.

Measure and estimate lengths

This video looks at how to measure objects including making sure that the measurement tool is lined up to start at zero.

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Example 1

What is the length of the line shown in the image?

This image shows a ruler in centimetres measuring a bar from 15 to 18 centimetres. Ask your teacher for more information.
Worked Solution
Create a strategy

Subtract the number at the starting point from the point where the bar ends.

Apply the idea

Starting at 15, we can see that the coloured bar ends at 18 centimetres.

\displaystyle \text{Length}\displaystyle =\displaystyle 18-15Subtract 15 from 18
\displaystyle =\displaystyle 3 \text{ cm}Evaluate
Idea summary

When measuring an object using a ruler, if the start of the object is at a number larger than zero, subtract the starting point from where the object ends on the ruler.

Estimate length

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Example 2

Choose the best estimate for the length of a train carriage.

20 metres
100 metres
Worked Solution
Create a strategy

Think about 1 metre as 1 large step. How many steps do you need to take to go from one end of a train carriage to the other?

Apply the idea

It would take about 20 large steps to go from one end of a train carriage to the other. So the best answer is option A.

Idea summary

1cm (centimetre) is about as big as your thumbnail.

1m (metre) is about as long as two normal steps (for an average Year 4 student).



measures, records, compares and estimates lengths, distances and perimeters in metres, centimetres and millimetres, and measures, compares and records temperatures

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