 Lesson

## Ideas

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.

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:

So, 43 + 12 = 55

Idea summary

Number lines can help us visualise the jumps between numbers

## Bridge to ten addition strategy

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

### 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

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.

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

### 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.

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:

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