1. Multiplication with Decimals
Reminder:
Multiplying with the grid method:
65 x 23
This can be re written as (60 + 5) x (20 + 3) 60 5 20 3
We now put this into the grid:
Add the answers
together: x
Multiply out
the numbers
to fill the
grid +
180
100 15 12 10 18 15
1495

2. Multiplication with Decimals
Now do these:
26 x x 59
86 x x 437
50 x x 649
35 x x 430 x +
240 40 12
1092 x
33,217 x
3200 +
240
3440 x
10,488 x 50
4000
4000 +
300
4300 x
588,643 x
2100 +
350
210 35
2695 x
, ,
, ,
247,680

3. Multiplication with Decimals
To multiply decimals we use the same method, but we have
to think about the place value:
To multiply as this is can cause confusion
so we think about the denomination
6.5 x 2.3
0.1 = 1 tenth
so 6.5 = 65 tenths
1.0 = 10 tenths
also 2.3 = 23 tenths
Therefore as long as we remember the denomination we can
multiply using the grid method:

4. Multiplication with Decimals
This answer was found by
multiplying tenths x tenths 20 3 x
180
100 15
1200
100
1 x 1 1
100
180 15 =
1495 1
100
So the denomination of the answer is
The numerical answer is 1495, so the place value of the 5 is 1
100
Therefore the correct answer in denomination of 1’s is:
14.95

5. Multiplication with Decimals
We can check that the answer is correct by estimating
6.5 x 2.3
Estimate to 7 x 3
= 14
Therefore we expect an answer about 14.
Inspect the answer 1495
If we put the decimal point here
1.495
the answer is clearly too small
If we put the decimal point here
149.5
the answer is clearly too big
The answer must be 14.95

6. Multiplication with Decimals
Now do these:
26 x x 5.9
8.6 x x 4.37
50 x x 64.9
3.5 x x 4.30 x +
240 40 12
109.2 x
33.217 x
3200 +
240
344.0 x
10.488 x 50
4000
4000 +
300
430.0 x
5,886.43 x
2100 +
350
210 35
26.95 x
, ,
, ,

7. Multiplication with Decimals
Points to note:
What happens when you have a number less than 1
multiplied by another number less than 1?
0.1 is called a decimal fraction
because it is written in decimal notation 10
Therefore 0.1 x 10 is finding 1 of 10 (a fraction of a quantity) 10
0.1 x 10 = 1
Therefore 0.1 x 0.1 is finding 1 of 1
1 x 1 = 1
100
0.1 x 0.1 = 0.01
When a number less than 1 is
squared the answer is even smaller
Therefore 0.12 = 0.01

8. Multiplication with Decimals
Now do these:
0.2 x
0.4 x
0.3 x
0.6 x
0.8 x x 0.6
0.06
0.16
0.08
0.25
0.09
0.36
0.18
0.49
0.56
0.9
0.04
0.008
0.09
0.064