2. Addition and subtraction

Lesson

Did you get the hang of adding 3 or 4 digit numbers together ?

Find the value of 720 + 250.

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 add numbers, we can break our numbers up (partition) and add the parts in a different order. Let's see how doing this helps us, in this video.

Let's find the value of 705 + 205, by partitioning the numbers.

a

Fill in the box with the missing number.

705 = 700 + ⬚

Worked Solution

b

Fill in the box with the missing number.

205 = ⬚ + 5

Worked Solution

c

Find the value of 705 + 205.

Worked Solution

Idea summary

Addition by partitioning involves splitting numbers into each place value. The place values are then added separately.

What happens with larger numbers? We can see in this video that writing our numbers down the page helps us with trading, or regrouping. Let's use a vertical algorithm to solve one.

Find the value of 6185 + 8282.

Worked Solution

Idea summary

Whenever we get more than 9 for one of the digits in our number, we have to regroup, or trade, to the next place value. All we need to remember is that we can trade 10 of any place for 1 of the places to the left.

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