Parents Guide to
Subtraction
This Power Point Presentation will
Show Parents the Language We Use
When Teaching Children Subtraction
Using Decomposition.

Organising numbers:
We organise numbers in columns like this:
H T U
Hundreds Tens Units
Only a single figure can go into each column.

9
Count up to 9
H T U
The units column is now full. You can only put one digit in each column. To make 10 we need to move to the next column.

3
0
The Tens Column
H T U
We have 3 in the tens column and nothing in the units column. The number is 30.

3
0
0
The Hundreds Column
H T U
We have 3 in the hundreds column and nothing in the tens or the units column. The number is 300.

Understanding Hundreds
Tens and Units
3
1
9
The number
319 is:
3 hundreds
1 ten
9 units
H T U

How to Take Away
Make sure the biggest number is on the top line.
305
- 24
---------

How to Take Away
Begin in the Units column.
Say:
5 take away 4 is 1
H T U
3 0 5
-
2 4
------------
1

How to Take Away
Move to the Tens column.
Say:
0 take away 2
You have nothing – so you can’t take away 2!
We need to EXCHANGE.
H T U
3 0 5
-
2 4
------------
1

How to Take Away:
Exchanging
You have to take 1 out of the hundreds column.
Remember:
You are taking 100 out of the hundreds column. 100 is the same as 10 tens!
H T U
3 0 5
-
2 4
------------
1
X 1 2
Now we have 2 hundreds and 10 tens!

We Exchanged 1
Hundred for 10 Tens
Now we say:
10 take away 2 is 8
There is no digit below the 2 in the hundreds column so we say:
2 take away 0 is 2.
H T U
2 3 0 5
-
2 4
------------
1
Answer: 281
2
8

Exchanging
When the digit on the top line is smaller than the digit on the bottom line we say:
‘We need to exchange.’

One More Example
H T U
5 6 7
-
3 2 9
------------

One More Example
7 is smaller than 9.
You have to take 1 out of the tens column.
Remember:
You are taking 10 out of the tens column. So the 7 becomes 17.
H T U
5 6 7
-
3 2 9
------------
8
X 1 5
Now we have 17 units and 5 tens!

One More Example
Now we say:
5 take away 2 is 3.
Move to the hundreds column.
Say:
5 take away 3 is 2.
Answer: 238
H T U
-
3 2 9
------------
8
2 3

Click Below to Return to
Our School Website.
We hope this powerpoint will help you to work with your child at home.
Please ask in school if you have any questions regarding our approach to teaching maths.
http://www.killeanps.com