Lesson

We're going to look at how addition and subtraction are related, and number lines can help us with that. Do you recall how to use a number line to work out subtraction problems ?

Use the number line to help you find the value of 35-24.

Worked Solution

Idea summary

To subtract one number from another, count the number of jumps between the numbers on the number line.

We can see how addition and subtraction are related by looking at their fact families, just like in this video.

Use the fact family of 5, 7 and 12.

a

What is 5+7?

Worked Solution

b

What is 12-7?

Worked Solution

c

What is 12-5?

Worked Solution

Idea summary

There are four different number sentences we can make for each fact family, two addition and two subtraction. If we start with the numbers, 12, 13 and 25, we can make the following fact family:

\begin{array}{c} 12+13=25 \\ 13+12=25\\ 25-13=25\\ 25-12=13 \end{array}

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