Topics
3. Addition
topic badge
AustraliaNSW
Stage 2

3.03 Addition strategies

Lesson
Practice
Lesson

Are you ready?

Remembering how we can solve  addition on a number line  can help us with our other addition strategies. Let's try now.

Examples

Example 1

Use the number line to help you find the value of 43 + 12.

404142434445464748495051525354555657585960
Worked Solution
Create a strategy

Start with the bigger number and count to the right by the smaller number.

Apply the idea

Locate where 43 is on the number line. We can find 43 + 12 by jumping from 43 to the right by 12:

404142434445464748495051525354555657585960

So, 43 + 12 = 55

Idea summary

Number lines can help us visualise the jumps between numbers

A number line from 0 to 20 with two points at 9 and 15 and an arrow to the right between the points

Bridge to ten addition strategy

Let's see how to change an addition problem using the bridge to ten strategy.

Loading video...

Examples

Example 2

How many more do we need to add to 9 to get to 10?

Worked Solution
Create a strategy

Use the bridge to 10 strategy.

Apply the idea
A row of ten squares, nine are shaded.

In the picture, we have 9 squares shaded. We need 1 more square to complete the pair to 10 squares.

So the bridge is 1. So we need to add 1 to get to 10:

9 + 1 = 10

Idea summary

Bridging to 10 can help us get to 10, so that adding can be much quicker.

Compensation addition strategy

The next video shows us how to use the compensation strategy to add more easily.

Loading video...

Examples

Example 3

If 7 + 10 = 17, what is the answer to 7 + 11?

Worked Solution
Create a strategy

Use the compensation strategy.

Apply the idea

If we look at 7 + 10 and 7 + 11, we can see that 10 has been changed to 11.

11 is 1 more than 10 as shown on the number line.

789101112131415

So we need to add 1 more to 7+10=17. To add 1 to 17 we can use a number line and find 17 and move 1 place to the right to get 18:

1213141516171819

So, 7 + 11 = 18

Idea summary

Compensation uses the answer of one problem, to find the answer to another problem.

Outcomes

MA2-5NA

uses mental and written strategies for addition and subtraction involving two-, three-, four and five-digit numbers

What is Mathspace

About Mathspace