2. Addition and subtraction

Lesson

Are you able to use a vertical algorithm to add numbers with no regrouping?

Find the value of 41+56.

Worked Solution

Idea summary

You might notice that sometimes the standard algorithm is called the 'vertical algorithm'. Let's think about why. When we use the standard algorithm, we line our numbers up in 'vertical' place value columns.

When we need to regroup to add or subtract, there are some different ways we can do this. Let's see how to solve an addition problem, then a subtraction problem.

Find the value of 997 - 648.

Worked Solution

Idea summary

We always start from the ones place, when we work down our page. If we don't have enough ones to subtract, we need to trade from the tens place. If we don't have enough tens to subtract, we need to trade from the hundreds place.

What happens with larger numbers? We can use a standard algorithm to solve addition and subtraction, as we see in this video.

Find the value of 2124 + 3351.

Worked Solution

Idea summary

When we are adding or subtracting down the page, it's really important to start from the right (ones place) and work to the left, no matter how many digits our numbers have.

When we need to do some trading, or regrouping, the standard algorithm helps us line up place value digits. Let's see how to add or subtract, when we need to regroup.

Find the value of 7263 - 2418.

Worked Solution

Idea summary

Each time we move one place to the left, the value of the digit is ten times bigger. This means we are able to regroup, or trade, to help us with addition and subtraction.

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