Multiplying and dividing by 2, 3, 4 and 8

In a nutshell

Multiplication and division by $2,3,4$ and $8$ is made simple through the use of times tables and by doubling and halving.

Multiplying

Being able to multiply by two and three means that you will find you can also multiply by other numbers such as $4,6$ and $8$ very easily.

Multiply by 2, 4 and 8

Multiplying by any one of these three numbers involves doubling - making two lots of something.

procedure

To multiply by $2$ : times by two (double) once.
To multiply by $4$ : times by two (double) twice.
To multiply by $8$ : times by two (double) three times.

Example

What is $6$ multiplied by $2,4$ and $8$ ?

Times by two once to get $6\times2$ :

$6\times2=6+6=\underline{12}$

Times by two twice to get $6\times4$ :

$\begin {aligned} 6\times2\times 2 =12\times2&=12+12=\underline{24} \end {aligned}$

Times by two three times to get $6\times8$ :

$\begin {aligned}6\times2\times2\times2 = 24\times2&=24+24=\underline{48} \end {aligned}$ 

Multiply by 3

To multiply by three means to make 'three lots of' something. Either recall the three times tables up to $3\times12$ that you already know, or add three lots of the number being multiplied together. The first twelve multiples of three are listed below.

$3,6,9,12,15,18,21,24,27,30,33,36$

Dividing

To divide means to share into equal parts.

Divide by 2, 4 and 8

Similar to multiplying, you can divide by two more than once to work out division by $4$ and $8$ .

Procedure

To divide by $2$ : divide by two (half) once.
To divide by $4$ : divide by two (half) twice.
To divide by $8$ : divide by two (half) three times.

Example

What is $32$ divided by $2,4$ and $8$ ?

Divide by two once to get $32\div2$ :

$32\div2=\underline{16}$

Divide by two twice to get $32\div4$ :

$32\div2\div2=16\div2=\underline8$

Divide by two three times to get $32\div8$ :

$32\div2\div2\div2=8\div2=\underline4$

Divide by 3

To divide by three means to share something into three parts. Once again, either recall the three times tables up to $3\times12$ that you already know, or separate the number one by one into three.

Example

Shelly wants to divide her pet fish into three tanks. She has $12$ fish. How many fish will there be in each tank?

The calculation is $12\div3$ . Start separating twelve fish into three equal groups.

Tank 1

Maths; Multiplication and division; KS2 Year 3; Multiplying and dividing by 2, 3, 4 and 8

Tank 2

Maths; Multiplication and division; KS2 Year 3; Multiplying and dividing by 2, 3, 4 and 8

Tank 3

Maths; Multiplication and division; KS2 Year 3; Multiplying and dividing by 2, 3, 4 and 8

Continue until all the fish are separated.

Tank 1

Tank 2

Tank 3

There will be four fish in each tank.

$12\div3=\underline{4}$