How_To_Be_Good_At_Math

108 CALCULATING •^ MULTIPLYING BY 10, 100, AND 1000

Multiplying by 10,

100, and 1000

Multiplying by 10, 100, and 1000 is straightforward. To multiply

a number by 10, for example, all you have to do is shift each

of its digits one place to the left on a place-value grid.

Move each digit

three places to

the left

Move each

digit two places

to the left

Move each

digit one place

to the left

To multiply a number

by 10, we just move

each of its digits one

place to the left.

Multiplying by 100

Let’s try multiplying 3.2 by 100

this time. To multiply a number by

100, we shift each digit two places

to the left. So, 3.2 becomes 320,

100 times bigger than 3.2.

Multiplying by 10

Let’s multiply 3.2 by 10. To work

out the answer, we just move each

digit one place to the left on the

place-value grid. So, 3.2 becomes

32, ten times bigger than 3.2.

Multiplying by 1000

Now let’s multiply 3.2 by

1000. To do this, we move each
      digit three places to the left. So,
      3.2 becomes 3200, 1000 times
      bigger than 3.2.

We can keep going like this

for 10 000, 100 000, and

even 1 000 000.

3. 
   

   2

   
   


4. 
   

   2

   
   


5. 
   

   2

   
   

32

320

3200

H

H

H

T

T

T

O

O

O

Th

Th

Th

Step to the left

Can you use the method we

have shown you to work out the

answers to these calculations?

6.79 × 100 =?

48 × 10 000 =?

TRY IT OUT

Answers on page 319

0.072 × 1000 =?

Add a 0 as a

place holder in

the ones column

Add two 0s as place

holders in the tens

and ones columns

1

10

1

10

1

10

108_109_Multiplying_by_10_100_1000_Multiplying_by_multiples_of_10.indd 108 29/02/2016 18:03