# Multiplication

## Multiplying decimals by 10, 100 and 1 000

When you multiply a decimal number by 10, all the numbers get 10 times bigger, so the decimal point moves one place to the right.

When you multiply by 100, all the numbers get 100 times bigger, so the decimal point moves two places to the right.

When you multiply by 1 000 all the numbers get 1 000 times bigger, so the decimal point moves three places to the right.

The following video shows you the correct method for multiplying decimal numbers by 10, 100 or 1 000:

Now try the following activity.

### Activity 28: Multiplying decimals by 10, 100, 1000

Calculate the following:

- 16.3 × 10
- 5.27 × 10
- 82.05 × 100
- 673.2 × 100
- 48.851 × 1 000
- 59.24 × 1 000

#### Answer

- 163
- 52.7
- 8 205
- 67 320
- 48 851
- 59 240

## Multiplying decimals

When multiplying decimal numbers, you should ignore the decimal point and use your usual method to multiply the numbers you are given.

When you have your answer, count up the total number of decimal places (or ‘dp’) in both of the numbers you have multiplied.

Starting from the right-hand column of your answer, count the same number of decimal places (dp) to the left and place your decimal point.

Watch the following video for an explanation of multiplying decimal numbers:

### Activity 29: Multiplying decimals

Complete this activity using the multiplication method you are most comfortable with. Show your answers to two decimal places (2 dp).

- 0.7 × 4
- 0.3 × 0.4
- 18.7 × 3
- 6.31 × 2.2
- 1.9 × 0.59
- 2.35 × 1.78
- Teabags cost £1.29 a box. How much will five boxes cost?
- Alun earns £8.95 an hour. How much does he earn for 37.5 hours?

#### Answer

- 2.8
- 0.12
- 56.1
- 13.882 (13.88 to 2 dp)
- 1.121 (1.12 to 2 dp)
- 4.183 (4.18 to 2 dp)
- £6.45
- £335.625 (£335.63 to 2 dp)