adding, subtracting, multiplying and dividing decimals for...
TRANSCRIPT
Adding, Subtracting, Multiplying and
Dividing Decimals for 4th Class
Welcome 4th Class to Decimal Operations.
Your lessons should be completed as follows:
Tuesday: Adding Decimals
Wednesday: Subtracting Decimals
Thursday: Multiplying Decimals
Friday: Dividing Decimals
Let’s Begin!
Today you will learn how to add
decimal numbers
When adding decimals, place value is very
important.
Write your numbers carefully!
The order that decimals come in is as follows:
Unit . Tenths Hundredths
Units come first, followed by the decimal
point.
Next come the tenths and finally the
hundredths
When adding decimals, keep the decimal
points under each other and don’t forget to
put the decimal point in your answer,
directly under the other decimal points.
Move onto the next page for an example
Add the following:
0.1 + 0.6
Write them underneath each other as follows
0.1
+ 0.6
0.7 Can you see that the decimal points are written right underneath
each other and that the decimal point in the answer is also
underneath?
This is important to get your place value right
Move on for another example
Add the following:
0.5 + 0.8
Again write your numbers underneath each other,
lining up the decimal points
0.5
+ 0.8
1.3
We simply add 5 and 8 to make 13 and put in the decimal
point under the others to change it to 1.3.
It is very important not to forget to put in
the decimal point at the end as we know
that 13 is a much bigger number than 1.3.
Without the decimal point our answer
would be completely wrong!
Now try some yourself on the next
page.
a. 0.3 + 0.5 =
b. 0.6 + 0.2 =
c. 0.5 + 0.4 =
d. 0.3 + 0.9 =
e. 0.6 + 0.9 =
f. 0.8 + 0.7 =
g. 0.7 + 0.4 =
Answers on the next page
a. 0.8
b. 0.8
c. 0.9
d. 1.2
e. 1.5
f. 1.5
g. 1.1
Continue on to learn how to add decimals with
whole numbers
The same rules apply here;
Keep all decimal points underneath each other
and don’t forget the decimal point in the
answer
Example: 5.63 + 2.97
Begin by writing the numbers under each other
This time we have units, tenths and
hundredths
Go to the next page for the solution
5.63
+ 2.97
8.60
In this example, when you add the hundredths 7 + 3, you
get 10
This means that you write down 0 and carry on 1, to add
to the tenths.
Now when you add the tenths, you add 1 + 9 +6 to get 16
This time write down 6 in the tenths position and carry on
1 to add to the units
Now when you add the units you are adding 1 + 2 + 5 to
make 8.
Don’t forget to put your decimal point in between the
units and tenths
a. 2.07 + 6.32
b. 5.93 + 2.61
c. 8.10 + 4.23
d. 7.08 + 2.31
e. 10.52 + 8.30
f. 23.64 + 56.78
g. 63.96 + 42.01
Answers on the next page
a. 8.39
b. 8.54
c. 12.33
d. 9.39
e. 18.82
f. 80.42
g. 105.97
You have now completed Tuesday’s work
Well Done
Today we will learn about subtracting
decimals
The rules for subtracting decimals are the same as for adding decimals
Place value is very important. Put units under units, tenths under tenths and hundredths
under hundredths.
Keep your decimal points under each other to help you
Then subtract in the usual way
3.9 – 2.3
First write your decimals underneath each
other
3.9
- 2.3
1.6
Don’t forget to put your decimal point in the
answer under the decimal points above it!
Now try some on the next page
a. 6.9 – 3.2
b. 7.8 – 1.3
c. 10.4 – 2.1
d. 9.8 – 8.6
e. 7.5 – 3.5
f. 6.4 – 4.2
Answers on the next page
a. 3.7
b. 6.5
c. 8.3
d. 1.2
e. 4.0
f. 2.2
Well done.
Move on for some more examples
In the next examples, the tenths and
hundredths in the top number may be
smaller than in the bottom number
7.52
- 2.43
Here we are going to borrow and pay back,
just like we do with normal subtraction
Move onto the next page where I will show you
7.52
- 2.43
5.09
I begin with the hundredths, by saying 2 take 3 I cannot
do, so I borrow 1 and make 12 at the top.
Now 12 take 3 leaves 9
I now move onto the tenths and first pay back the 1
that I borrowed. I add this to 4 to make 5.
Now I say 5 take 5 leaves 0
I now move onto the units and say 7 take 2 leaves 5
Finally I put the decimal point between the units and
tenths
Try some yourself on the next page
a. 4.51 – 2.23
b. 8.76 – 5.39
c. 7.77 – 3.69
d. 9.82 – 6.34
e. 10.43 – 7. 29
Answers on the next page
a. 2.28
b. 3.37
c. 4.08
d. 3.48
e. 3.14
Well done!
You have now completed Wednesday’s work
Today you will learn how to multiply
decimals
When we want to put the decimal point in the
correct place in our answer, we go back to
our question and count the numbers after
the decimal point.
Our answer has to have the exact same amount
of numbers after the decimal point
Go onto the next page and I will show you
what I mean with an example
0.3 x 3
Begin by writing them under each other
0.3
x 3
Ignore the decimal point and first multiply all
the numbers in the top line by 3
0.3
x 3
0 9
0.3
x 3
0 9
We now need to decide where the decimal
point goes in the answer, so we look at our
number that was multiplied (0.3) and see
that there was only one number after the
decimal point
This means that there must only be one
number after the decimal point in our
answer, so I will put the decimal point
between 0 and 9
0.3
x 3
0.9
The correct answer is 0.9
See another example on the next page
0.6 x 4
Begin by writing the numbers underneath each other
0.6
x 4
Now multiply all the numbers in the top line by 4
When I multiply 6 by 4, I get 24.
So I write down 4 under the tenths and carry on 2.
0.6
x 4
4
Now when I multiply 0 by 4, I get 0. I add
on the 2 that I carried on
0 + 2 is 2 and I write this under the units.
0.6
x 4
2 4
This is just like normal multiplication
0.6
x 4
2 4
Now I need to decide where to put the decimal
point so I look at the number I was
multiplying (0.6) and I see that there was
one number after the decimal point
So in my answer there has to be one
number after the decimal point also;
0.6
x 4
2.4
So I will put the decimal point in between 2
and 4
The correct answer is 2.4
Your turn to try some on the next page
a. 0.2 x 4
b. 0.5 x 2
c. 0.6 x 5
d. 0.8 x 7
e. 1.5 x 3
f. 2.4 x 6
Answers on the next page
a. 0.8
b. 1.0
c. 3.0
d. 5.6
e. 4.5
f. 14.4
Move onto the next page to learn some more
about multiplying decimals
5.62 x 4 Begin by writing the numbers under each
other 5.62 x 4
Now multiply all the numbers on top by 4 Start by multiplying 2 by 4
5.62 x 4 8
Now move onto multiplying 6 by 4
5.62 x 4 48
This gives 24, so write down 4 and carry 2.
Now multiply 5 by 4 to get 20 Add in the 2 you carried on to give 22
5.62 x 4
22 48
5.62
x 4
22 48
To decide where to put the decimal point, go
back to the number you multiplied (5.62) and
count the numbers after the decimal point.
There are 2 numbers after the decimal point so
you must also have 2 numbers after the
decimal point in the answer
5.62
x 4
22.48
The correct answer is 22.48
Now you try some on the next page
a. 2.36 x 3
b. 5.01 x 5
c. 4.96 x 2
d. 8.51 x 4
Answers on the next page
a. 7.08
b. 25.05
c. 9.92
d. 34.04
Well done on completing Thursday’s work
Today you will learn how to divide
decimals
The rules for dividing are the same as for
adding and subtracting.
Keep your decimal points under each other
Let me show you an example on the next page
4.2 ÷ 2
Write the sum as follows
2 4.2
Now continue by dividing the first number (4)
by 2. This gives 2 so write this under the 4
2 4.2
2
2 4.2
2
Remember to keep the decimal point in the
answer under the decimal point in the
number above it.
Putting in the decimal point now looks like this
2 4.2
2.
Now continue dividing the next number.
2 divided by 2 gives 1
Now write this under after the decimal point
2 4.2
2.1
The answer is 2.1
Try some for yourself on the next page
a. 6.8 ÷ 2
b. 8.4 ÷ 4
c. 9.9 ÷ 3
d. 4.8 ÷ 4
e. 6.6 ÷ 3
Answers on the next page
a. 3.4
b. 2.1
c. 3.3
d. 1.2
e. 2.2
Now move on for some more division examples
12.9 ÷ 3
Write the number as follows;
3 12.9
Begin by dividing the first number by 3
1 ÷ 3 cannot be done because 1 is smaller than 3
Whenever this happens with a number, combine it with the number beside it
to make a larger number.
When I combine 1 with 2, I can make 12
3 12.9
Now 12 ÷ 3 makes 4.
Write this under the 2 in the upper line
3 12.9
4
Decimal points are written under decimal
points, so put that in next
3 12.9
4.
Now continue by dividing 9 by 3 to get 3.
Write this down after the decimal point
3 12.9
4.3
The answer is 4.3
Move on for another example
6.27 ÷ 3
Begin by writing the sum as follows;
3 6.27
Divide the first number 6 by 3. This gives 2.
Write this answer in under the number 6
3 6.27
2
Keeping the decimal points under each other
means that the decimal point should be
written next.
3 6.27
2.
Continue on with dividing the next number by 3
3 6.27
2.
We can see that the next number, 2, can’t be
divided by 3 as it is too small, so we put 0
after the decimal point and then combine 2
and 7 to make 27
3 6.27
2.0
Now 27 divided by 3 makes 9
3 6.27
2.09
The answer is 2.09
Try some on the next page
a. 4.16 ÷ 2
b. 81.9 ÷ 9
c. 7.56 ÷ 7
d. 6.39 ÷ 9
e. 9.27 ÷ 3
Answers on the next page
a. 2.08
b. 9.1
c. 1.08
d. 0.71
e. 3.09
Well done! Friday’s work is complete
Have a nice weekend everyone.
Get some fresh air and exercise and remember to keep social distancing and washing your
hands
If you have any worries about the maths I have given you can contact me at
Just do your best and keep up the good work!