 Lesson

## Ideas

Do you remember some of the methods, or strategies, we've used to  add numbers together?

### Examples

#### Example 1

765 + 104 = 869. Use this to fill in the gaps in the number sentences.

a

665+ ⬚ = 869

Worked Solution
Create a strategy

Use the given number sentence to find the pattern.

Apply the idea

Comparing the number sentences: 765 +104 = 869 and 665 + ⬚ = 869, we notice that they have the same sum of 869. The first numbers 765 and 665 differ by 100. So we need to add 1 hundred to 104.

Add the digits in each place value column.

665+204=689

b

565+ ⬚ = 869

Worked Solution
Create a strategy

Use the number sentence from the previous part to find a pattern.

Apply the idea

Comparing the number sentences: 665 +204 = 869 and 565 + ⬚ = 869, in the first number of each statement the number of hundreds differ by 1, so we need to add 1 hundred to 204.

Add the digits in each place value column.

565+304=869

Idea summary

We can use patterns to add two numbers. If we are given one number sentence, and need to complete another, then we can compare the number sentences to find a pattern to help.

## Addition of more than two numbers

What happens when we have more than two numbers to add together? Let's see how we might approach a problem like this, in the following video.

### Examples

#### Example 2

Find the value of 540 + 44 +5.

Worked Solution
Create a strategy

Use a place value table.

Apply the idea

Write the numbers in the place value table.

Add the digits in each place value column.

540 + 44 + 5 = 589

Idea summary

We can use a place value table when adding more than two numbers. We add the numbers in each column starting from the units place value.

If we have a written problem, it helps to know which words relate to addition. Looking for clues helps us find out what we need to add, as we can see in this video.

### Examples

#### Example 3

In a family, the grandmother is 73 years old, the mother is 32 years old, and the daughter is 4 years old. What is the combined age of the family?

Worked Solution
Create a strategy

The word "combined" means addition. So we need to add the ages.

Apply the idea

The combined age of the family is 109 years.

Idea summary

There are some words we might come across that mean we will be using addition whereas other words may suggest subtraction. This is not a complete list, so we need to understand the context of the question, to work out whether to add or subtract.

### Outcomes

#### VCMNA209

Select and apply efficient mental and written strategies and appropriate digital technologies to solve problems involving all four operations with whole numbers and make estimates for these computations

#### VCMNA219

Continue and create sequences involving whole numbers, fractions and decimals. Describe the rule used to create the sequence