When we are asked to add or subtract numbers such as 125 + 75 or 125 - 25, we can often work out the answer mentally.

However, when we are given questions with bigger numbers, we usually need to use a written method.

In this activity, we will use the **columnar method** to **add and subtract numbers.**

Let's have a look at how we can use the method to add **362 + 623**

First, we write the numbers in columns** under the correct unit **(hundreds, tens, ones).

It can help to put the biggest number on the top (when adding)

Remember to include **a + sign **so that you know that you are **adding.**

**H T O**** **

*623* ** **

__362__

Starting at the right-hand column (the ones), we add each column and write the answers underneath.

**H T O**** **

*623*

__362__

**985**

**362 + 623 = 985**

Here is another example. This time we will need to **carry over **or **exchange.**

Remember to include the **+ sign** so you know what you're trying to do!

**H T O**** **

**4 2 5**** **** **

**5 5 7**

**9 8****12**

First, **the ones:** 5 + 7 = 12

We can partition this into 10 and 2

The ten moves into the tens column and waits on the doorstep (see the small **1** which represents 1 ten).

The 2 stays in the ones column.

**425 + 557 = 982**

Now let's look at **subtraction.**

**564 - 352 **

*Remember to write a - sign so that you don't forget that this is subtraction!*

**H T O**** **** **

**564**

__352__

**212**

Again, we start with the ones column, but this time we** subtract** the bottom number from the top (4 - 2 is not the same as 2 - 4).

It is important that we remember this!

**564 - 352 = 212**

Now, let's have a go at subtracting with **exchanging**, also known as **borrowing.**

Again, remember to put the - sign so you don't forget that you're subtracting!

**H T O**** **

**45 14 7 **

** 1 5 3**

** 3 9 4**

First, the ones: 7 - 3 = 4

Next, the tens: 4 tens - 5 tens we can't do, so we exchange (or borrow) one hundred for 10 lots of ten. This means that we now have only 4 hundreds in the hundreds column and 14 tens in the tens column.

14 tens - 5 tens = 9 tens (or 140 - 50 = 90). We write this in the tens column as 9.

Finally, the hundreds: we now have 4 hundreds - 1 hundred = 3 hundreds ( or 400 - 100 = 300). We write this as 3 in the hundreds column.

Our answer is 393

Phew, that was a lot to do!

Now, it's your turn to have a go using this method to add and subtract numbers. Good luck!