Topics
10. Measurement
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Australia
Year 3

10.02 Order and compare lengths

Lesson
Practice
Lesson

Are you ready?

Can you  order 2 or 3 digit numbers  ?

Examples

Example 1

Order these numbers from largest to smallest.

a

73, \, 33, \, 37

Worked Solution
Create a strategy

We should order the tens first, then the ones.

Apply the idea

The numbers in the place value table are shown:

TensOnes
73
33
37

37 and 33 have the same smallest tens digit, so they are smaller than 73.

But 33 has the smaller ones digit, so 33 is smaller than 37.

The numbers from largest to smallest are: 73,\,37,\, 33

b

671, \, 167, \, 617

Worked Solution
Create a strategy

We should order the hundreds first, then the tens, then the ones.

Apply the idea

The numbers in the place value table are shown:

HundredsTensOnes
671
167
617

167 has the smallest hundreds digit so it is the smallest number.

671 and 617 have equal hundreds digits, but 617 has the smaller tens digit.

The numbers from largest to smallest are: 671,\,617,\, 167

Idea summary

When we use place value to order numbers, always start with the far left digit and think about the digit's place value.

Compare lengths

This video uses an example of tablet screen sizes and compares lengths using a number line.

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Examples

Example 2

Glen is 165 cm tall. Valentina is 144 cm tall. Who is taller?

Worked Solution
Create a strategy

Plot the two values on a number line.

Apply the idea

The heights are plotted on the number line below:

140145150155160165170

The taller person will have the larger height which will lie on the right of the number line. Based on the number line, 165 is larger than 144.

So Glen is taller than Valentina.

Idea summary

We can use a number line to compare measurements by plotting the values. The further the number is to the right of 0, the larger the number is.

Order by length

This video shows how we can compare numbers, if the unit of length are the same, to order by length.

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Examples

Example 3

A shark is 6 m long, a boat is 19 m long, a dolphin is 3 m long, a ship is 25 m long and a whale is 14 m long.

Choose the list that puts the items in order from shortest to longest.

A
Dolphin, Shark, Whale, Boat, Ship
B
Whale, Dolphin, Ship, Boat, Shark
Worked Solution
Create a strategy

We should order the ones first, then the tens.

Apply the idea

The numbers in the place value table are shown:

TensOnes
6
19
3
25
14

3 has a smaller ones value than 6, making it the smallest number.

19 and 14 have equal tens digits, but 14 has the smaller ones digit.

25 has the largest tens digit so it is the largest number in the list.

So the numbers from smallest to largest are: 3, \, 6, \, 14, \, 19, \, 25

The list in order from shortest to longest should be: Dolphin, Shark, Whale, Boat, Ship

The correct answer is A.

Idea summary

When we compare lengths, make sure the values use the same units of measurement. For example, all lengths are in centimetres.

Outcomes

ACMMG061

Measure, order and compare objects using familiar metric units of length, mass and capacity

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