 # 7.02 Number sentences from story problems

Lesson

## Ideas

Remembering how to  equally share  a number into groups can help us in this lesson. Let's try this problem to review.

### Examples

#### Example 1

Complete the statement with the missing number.

If you get 8 groups of , then altogether you have 80.

Worked Solution
Create a strategy

Rewrite the problem as a number sentence.

Apply the idea

We can write the problem as a number sentence: 8\times⬚=80 Which can also be written as: 80\div8=⬚

To divide 80 by 8, count up by 8 to get to 80: 8, \, 16, \, 24, \, 32, \, 40, \, 48, \, 56, \, 64, \, 72, \,80.

We needed to count up ten times so: 80\div 8 = 10 which means: 8\times 10=80

So the completed statement is:

If you get 8 groups of 10, then altogether you have 80.

Idea summary

We can rewrite story problems as a division or a multiplication to find the unknown in the problem.

## Multiplication story problems

How do we know if we need to multiply? Let's see how to solve this story problem.

### Examples

#### Example 2

There were 2 rows of trees in a field, with 3 trees in each row.

Write a number sentence for this story problem to find the total number of trees in the field.

Worked Solution
Create a strategy

Since there are an equal number of trees in each row, we can think of each row as a group.

Apply the idea

There were 2 groups of 3 trees, and "groups of" means multiply.

Number sentence =2\times3

Idea summary

If we need to find the total for multiple equal groups, we need to multiply.

## Division story problems

When our story has some sharing, it's time for division, as we see in this video.

### Examples

#### Example 3

Dylan has 120 chocolates to give out to 10 guests at his birthday party and wants to make sure each guest gets the same amount.

Write a number sentence for this story problem to find how much each guest would get.

Worked Solution
Create a strategy

Dylan needs to equally share the chocolates, so we need to use division.

Apply the idea

Dylan needs to share or divide 120 chocolates into 10 equal groups. So he needs to divide 120 by 10.

Number sentence =120\div 10

Idea summary

If we know our total and want to find out how many groups we have, or how many are in each group, we need to divide.

For story problems, we need to look for key words that tell us what we need to do.

### Outcomes

#### MA2-8NA

generalises properties of odd and even numbers, generates number patterns, and completes simple number sentences by calculating missing values