Parents Guide to Subtraction

1
Parents Guide to Subtraction

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

2
Organising numbers

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

3
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.
4
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.
5
The Hundreds Column

• 3
• 0
• 0

H T U
We have 3 in the hundreds column and nothing in
the tens or the units column. The number is 300.
6
Understanding Hundreds Tens and Units

• 3
• 1
• 9

H T U
The number 319 is 3 hundreds 1 ten 9 units
7
How to Take Away

• Make sure the biggest number is on the top line.
• 305
• - 24
• ---------

8
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

9
How to Take Away

• Move to the Tens column.
• Say
• 0 take away 2
• You have nothing so you cant take away 2!
• We need to EXCHANGE.

• H T U
• 3 0 5
• 2 4
• ------------
• 1

10
How to Take Away Exchanging

• You have to take 1 out of the hundreds column.

• H T U
• 3 0 5
• 2 4
• ------------
• 1

Remember You are taking 100 out of the hundreds
column. 100 is the same as 10 tens!
X
1
2
Now we have 2 hundreds and 10 tens!
11
We Exchanged 1 Hundred for 10 Tens

• Now we say
• 10 take away 2 is 8

• H T U
• 3 0 5
• 2 4
• ------------
• 1

2
1
X
There is no digit below the 2 in the hundreds
column so we say 2 take away 0 is 2.
Answer 281
2
8
12
Exchanging

• When the digit on the top line is smaller than
  the digit on the bottom line we say
• We need to exchange.

13
One More Example

• H T U
• 5 6 7
• 3 2 9
• ------------

14
One More Example

• 7 is smaller than 9.
• You have to take 1 out of the tens column.

• H T U
• 5 6 7
• 3 2 9
• ------------
• 8

Remember You are taking 10 out of the tens
column. So the 7 becomes 17.
X
1
5
Now we have 17 units and 5 tens!
15
One More Example

• Now we say
• 5 take away 2 is 3.

• H T U
• 5 6 7
• 3 2 9
• ------------
• 8

5
1
X
Move to the hundreds column. Say 5 take away 3
is 2.
Answer 238
2
3
16
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