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

scoilfhursalyre@yahoo.ie

Just do your best and keep up the good work!