2. Addition and subtraction

Lesson

Do you remember how we can round numbers , to help us simplify some number problems?

Round 3322 to the nearest thousand.

Worked Solution

Idea summary

To round a number to the nearest 1000, plot it on a number line and choose the multiple of 1000 that it is closest to.

When we solve addition and subtraction problems, estimating our answer gives us an idea of what to expect. In this video, we see how we can estimate the answer to addition or subtraction problems, using a number line to help us.

We want to estimate the answer to 258-26.

a

Round each of the two numbers to the nearest and then subtract them.

Worked Solution

b

Find the value of 258-26.

Worked Solution

Idea summary

If we don't need an exact answer to a problem, we can use estimating to find out a close-enough answer. We can also use estimating to check our answers, so it is a great skill to learn.

How can we solve a problem with more than one part? Have a look at this video to see some different ways to do this.

Find the value of 570+25+4.

Worked Solution

Idea summary

By adding in a different order, we may be able to use strategies such as Bridge to 10, to help us solve a problem. The number lines below show how we can solve 7 + 5 + 3 by changing the order, and still arrive at the same answer of 15.

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

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