Transcript Parents Guide to Subtraction Using Decomposition

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
Hundreds Tens
U
Units
Only a single figure can go into each
column.
Count up to 9
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.
The Tens Column
3
0
H
T
U
We have 3 in the tens column and nothing in the units column. The
number is 30.
The Hundreds Column
3
0
0
H
T
We have 3 in the hundreds column and nothing in the tens or the
units column. The number is 300.
U
Understanding Hundreds
Tens and Units
3
The number
1 319 is:
9
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
HTU
3 0 5
24
-----------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.
HTU
3 0 5
24
-----------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!
X 1
HTU
3 0 5
24
-----------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.
Answer: 281
HTU
2X 1
3 0 5
24
-----------1
2
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.
X 1
HTU
5 6 7
3 2 9
-----------8
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
HTU
5 56X 17
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