Transcript how to multiply PPT File

Welcome To
Multiplication
Wednesday 5th October 2016
If you can dream it, you can do it!
Lower School Methods
Multiplication is simply repeated
addition:
2 x 3 = 2 lots of 3
or 3 + 3 = 6
If your child has to do 3 x 5 =
They can do 3 lots of 5 or
5+5+5=
Can you do 5 x 6 = as repeated
addition?
6+6+6+6+6= 30 cans
5 x 6 = 30 cans
You can also use an
array…
An array is where you arrange the
numbers in rectangles:
To do 2 x 6 =, we can draw 2 rows
of 6 and we get the answer 12.
This is called an array.
To do 3 x 4 =, we can draw 3 rows
of 4 and we get the answer 12.
Can you draw 3 x 6 = as
an array?
Upper School Methods
We do 2 methods:
1. The grid method
2. The formal algorithmic method.
The Grid Method
To do 3 x 43 we partition the large
number:
X
3
40
3
The Grid Method
To do 3 x 43 we partition the large
number:
X
3
40
120
3
9
add them
to get 129.
The Grid Method
To do 32 x 43 we partition both
numbers:
X
30
2
40
3
The Grid Method
To do 32 x 43 we partition both
numbers:
X
30
2
40
1200
3
90
The Grid Method
To do 32 x 43 we partition both
numbers:
X
30
2
40
1200
80
3
90
6
The Grid Method
To do 32 x 43 we partition both
numbers:
X
30
2
40
1200
80
3
90
6
=1290
= 86
The Grid Method
To do 32 x 43 we partition both
numbers:
X
30
2
40
1200
80
3
90
6
1290
+ 86
1376
The Grid Method
Can you do 25 x 32?
The Grid Method
Can you do 25 x 32?
X
20
5
30
600
150
2
40
10
640
+ 160
800
The Formal Method
To do 3 x 45 we write it vertically:
45
X 3
5
We do units first 3x5=15. We write in
the 5 and carry the 1 into the tens
column.
1
The Formal Method
To do 3 x 45 we write it vertically:
45
X 3
135
Then we do 3x4=12 and add on the 1 to
make 13. The answer is 135.
1
The Formal Method
To do 23 x 45 we write it vertically:
45
X 23
135
We do units first 3x5=15. We write in the 5
and carry the 1 into the tens column. Then
we do 3x4=12 and add on the 1 to make
13. The answer is 135.
1
The Formal Method
We then do the tens – 20 x 45:
45
X 23
135
0
We put a place-bearer (a zero) in the units
column and then do 2x5 …
1
The Formal Method
We then do the tens – 20 x 45:
45
X 23
135
900
We do 2x5 and carry the one ten, followed
by 2 x 4 and add the 1 to make 9 or 900
in all.
1
The Formal Method
45
X 23
135
900
1035
We then add 135 to 900 and get… 1035.
1
The Formal Method
Can you do 53 x 65 ?
53
X 65
The answer is 135.
The Formal Method
Can you do 53 x 65 ?
53
X 65
265
3180
3445
The answer is 3445.