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Maths Zone by Mandy Barrow

 
 
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Literacy : Science : Maths
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Multiplication Tricks

On this page you will learn some tricks which will help you

6 times table

Multiplying by 4 | Multiplying by 8

Multiplying by 9 or 99 or 999 | Multiplying by 11

Multiplying by doubling and halving

You may like to use a calculator when investigating these tricks.

x 0 1 2 3 4 5 6 7 8 9 10 11 12
0 0 0 0 0 0 0 0 0 0 0 0 0 0
1 0 1 2 3 4 5 6 7 8 9 10 11 12
2 0 2 4 6 8 10 12 14 16 18 20 22 24
3 0 3 6 9 12 15 18 21 24 27 30 33 36
4 0 4 8 12 16 20 24 28 32 36 40 44 48
5 0 5 10 15 20 25 30 35 40 45 50 55 60
6 0 6 12 18 24 30 36 42 48 54 60 66 72
7 0 7 14 21 28 35 42 49 56 63 70 77 84
8 0 8 16 24 32 40 48 56 64 72 80 88 96
9 0 9 18 27 36 45 54 63 72 81 90 99 108
10 0 10 20 30 40 50 60 70 80 90 100 110 120
11 0 11 22 33 44 55 66 77 88 99 110 121 132
12 0 12 24 36 48 60 72 84 96 108 120 132 144

Multiplying by six

This works for even numbers only.

6x2 = 12

6x4 = 24

6x6 = 36

6x8 = 48


The number you are multiplying by is always the number in the units column. 6x2 = 12

The tens column is always half the number in the units column.

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Multiplying by Eight

Multiplying by 8 can be achieved by doubling three times:

Example:

Q. What is 742 x 8?
A. 742 x 2 = 1484
.....1484 x 2 = 2968
.....2968 x 2 = 5936

The answer is 5936

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Multiplying by Nine by Jo and Kimberley

Hold both hands up in front of you with your palms facing you.

Whatever you're multiplying by (say 8) bend down that finger.
(The 8th from left to right)

The fingers to the left of the bent finger are the tens (7) and to the right the units (2).

The answer ot 8 x 9 is there for 72.

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11 x 9 is easy

12 times nine is just a little mnemonic.

12 is 10 + 2

remember the 2

2x9 = 18

just stick a 0 in the middle

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Here is another trick

Whatever you re multiplying by 9, the tens of the answer is always one less.

eg. 8x = 70 something 4x = 30 something and so on

The digits in the answers of the 9 times table always add up to 9.

 

(The tens and units ALWAYS ad up to 9 !)

eg. 7 x 9 = 60 something

6 + ? = 9

so 7x 9 =63

Another method of multiplying by 9

Multiplying by 9 is really multiplying by 10 and taking away you are multiplying.

So, 8×9 is just 8×10-8 which is 80-8 or 72.

Let’s try a harder example: 46×9 = 46×10-46 = 460-46 = 414.

One more example: 68×9 = 680-68 = 612.

Multiplying by 99, or 999 is similar

To multiply by 99, you multiply by 100 and taking away you are multiplying.

So, 46×99 = 46x 100 - 46 = 4600-46 = 4,554

To multiplying by 999, you multiply by 1000 and taking away you are multiplying.

38×999 = 38x1000-38 = 38000-38 = 37,962

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 Multiplying by Eleven
The eleven times table has always been very easy to learn up to 9 x 11.

Here's a way of multiplying large numbers by 11 too:

To multiply any number of two figures by 11:
Example:

Q. What is 34 x 11 ?
A. Add the first and second digits ... 3 + 4 = 7;
....Place the answer between the the first and second digits ..... 374

The answer is 374.

NB. When the sum is of the first and second digits is more than 9, increase the left-hand number by the 1 to carry.

Example:

Q. What is 98 x 11 ?
A. Add the first and second digits ... 9 + 8=17
....Add 1 to 9 to get 10
....Place the 7 between the 10 and 8

The answer is 1,078

To multiply any number of three figures by 11:
You add pairs of numbers next to each other, except for the numbers on the edges.

Example:

Q. What is 324 x 11 ?

A. Write down the first digit ... 3
.......Add the first and second digits ... 3 + 2 = 5
.......Add the second and third digits .. 2 + 4 = 6
.......Write down the last digit ........... 4

The answer is 3564.

Does it work for all three digit numbers?

To multiply any number of four figures by 11:

Q. What is 3254×11 ?

A. Write down the first digit ... 3
.......Add the first and second digits ... 3 + 2 = 5
.......Add the second and third digits .. 2 + 5 = 7
.......Add the third and fourth digits .. 5 + 4 = 9
.......Write down the last digit ........... 4

The answer is 35794.

Remember when the sum is of the first and second digits is more than 9, increase the left-hand number by the 1 to carry.

An example involving carrying:

Q. What is 4657 × 11 ?

A. Write down the first digit ... 4
.......Add the first and second digits ... 4 + 6 = 10
.......Add the second and third digits .. 6 + 5 = 11
.......Add the third and fourth digits .. 5 + 7 = 12
.......Write down the last digit ........... 7

Going from right to left write down 7

Notice that 5 + 7 = 12

Write down 2 and carry the 1

6 + 5 = 11, plus the 1 you carried = 12

So, write down the 2 and carry the 1

4 + 6 = 10, plus the 1 you carried = 11

So, write down the 1 and carry the 1

To the left most digit, 4, add the 1 you carried

So, 4657 × 11 = 51,227

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Multiplying by doubling and halving

When you’re multiplying two numbers together and one of the numbers is even, you can divide that number by two and multiply the other number by 2. You can do this over and over until you get to multiplication this is easy for you to do.

Q. What is 14 x 16?

A. Double one number and halve the other number

14×16 = 28×8

This is still to hard for me so double one number and halve the other number again

28×8 = 56×4

This is still to hard for me so double one number and halve the other number again

56×4 = 112×2

Now that is easier for me.

112×2 = 224

Here is another example:

Q. What is 12 × 15?

A. 12×15 = 6×30

6×30 s the same as 6×3 with a 0 at the end so the answer is 180.

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© Copyright Mandy Barrow 2013

Mandy left Woodlands in 2003 to work in Kent schools as an ICT Consulatant.
She now teaches computers at The Granville School and St. John's Primary School in Sevenoaks Kent.

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