Topics
3. Addition
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Australia
Year 3

3.02 Counting on

Lesson
Practice
Lesson

Are you ready?

Do you remember how to  count forward  by 10?

Examples

Example 1

What is 20 + 10?

Worked Solution
Create a strategy

Put the numbers in a place value table and add the values in each column.

Apply the idea

Put the numbers in a place value table and add the numbers in each column:

TensUnits
20
10

Add the smallest place value first. So 0 + 0 makes 0.

TensUnits
20
+10
0

Then add the next place value. 2 + 1 would make 3.

TensUnits
20
+10
30

So 20 + 10 = 30.

Idea summary

To add numbers we can use a place value table.

Count on by 1 and 2

Let's see how we can count on by 1, and then 2. What patterns do we make?

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Examples

Example 2

Write the next number in the pattern:

1,\,3,\,5,\,7,\,9,\, 11,\,⬚

Worked Solution
Create a strategy

Get the next value by counting on to complete the pattern.

Apply the idea

Count on from 1 to 3 to get the increase of 2 as shown in the number line.

A number line with a point at 1 and an arrow pointing to 3.

So to get the next number in the pattern, we need to count on from 11 by 2. We can add them together using a place value table.

TensUnits
11
+02
13

The next number in the pattern is 13:1,\,3,\,5,\,7,\,9,\, 11,\,13

Idea summary

When we count on by 1, and then 2, we can make patterns of odd or even numbers.

Count on by 5 and 10

What patterns do you see if we count by 5, or 10?

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Examples

Example 3

Write the next number in the pattern:

3,\,8,\,13,\,18,\,23,\, 28,\, ⬚

Worked Solution
Create a strategy

Get the next values by counting on to complete the pattern.

Apply the idea

Count on from 3 to 8 to get the increase of 5. As shown in the number line below.

012345678910

So to get the next number in the pattern, we need to count on from 28 by 5. We can add them together using a place value table.

TensUnits
28
+05
33

The next number in the pattern is 33:3,\,8,\,13,\,18,\,23,\, 28,\, 33

Idea summary

When we count on, we can use the pattern to help us work out the next number.

Outcomes

AC9M3N07

follow and create algorithms involving a sequence of steps and decisions to investigate numbers; describe any emerging patterns

AC9M3A02

extend and apply knowledge of addition and subtraction facts to 20 to develop efficient mental strategies for computation with larger numbers without a calculator

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