G S Rehill's Interactive Maths Software Series - "Building a Strong Foundation in Mathematics" from mathsteacher.com.au.

Order a 12-month Year 7 Interactive Maths software Homework Licence for only $19.95. Order a 12-month Year 8 Interactive Maths software Homework Licence for only $19.95. Order a 12-month Year 9 Interactive Maths software Homework Licence for only $19.95. Order a 12-month Year 10 Interactive Maths software Homework Licence for only $19.95.

Year 7 Interactive Maths - Second Edition


Multiplication of Decimals

In this section, we will consider the multiplication of a decimal by a whole number, multiplication of a decimal by a power of ten, multiplication of a decimal by a multiple of a power of ten and multiplication of a decimal by another decimal.


Multiplication of a Decimal by a Whole Number

Multiplication is repeated addition.

This can be represented on the number line as follows:

The number line represents multiplication as repeated addition.


Note the following:

Note that there is 1 decimal place in the number being multiplied and so there is 1 decimal place in the answer.


This suggests that:

To multiply a decimal number by a whole number:

  • ignore the decimal point and multiply the digits
  • place the decimal point in the answer so that it has the same number of decimal places as the number being multiplied


Example 11

Calculate 45.27 6.

Solution:

Note that there are 2 decimal places in the number being multiplied and so there are 2 decimal places in the answer.


Note:

There are two decimal places in the decimal number being multiplied.  So, we place the decimal point two places from the right-hand end of the answer.


Example 12

Calculate 7.382 5.

Solution:

Note that there are 3 decimal places in the number being multiplied and so there are 3 decimal places in the answer.


Note:
  • There are three decimal places in the decimal number being multiplied.  So, we place the decimal point three places from the right-hand end of the answer.
  • Any trailing zeros in the decimal places of the answer can be omitted.

In general:

If there are n decimal places in the decimal number being multiplied, then place the decimal point n places from the right-hand end of the answer.


Example 13

Calculate 0.0005 8.

Solution:

Note that there are 4 decimal places in the number being multiplied and so there are 4 decimal places in the answer.


Note:
  • There are four decimal places in the decimal number being multiplied.  So, we place the decimal point four places from the right-hand end of the answer.
  • Any trailing zeros in the decimal places of the answer can be omitted.


Example 14

Calculate 47.4 45.

Solution:

Note that there is 1 decimal place in the number being multiplied and so there is 1 decimal place in the answer.


Note:
  • There is one decimal place in the decimal number being multiplied.  So, we place the decimal point one place from the right-hand end of the answer.
  • Any trailing zeros in the decimal places of the answer can be omitted.

| Home Page | Order Maths Software | About the Series | Maths Software Tutorials |
| Year 7 Maths Software | Year 8 Maths Software | Year 9 Maths Software | Year 10 Maths Software |
| Homework Software | Laptop Schools | Tutor Software | Maths Software Platform | Trial Maths Software |
| Feedback | About mathsteacher.com.au | Terms and Conditions | Our Policies | Links | Contact |

Copyright 2000-2014 mathsteacher.com Pty Ltd.  All rights reserved.
Australian Business Number 53 056 217 611

Copyright instructions for educational institutions

Please read the Terms and Conditions of Use of this Website and our Privacy and Other Policies.
If you experience difficulties when using this Website, tell us through the feedback form or by phoning the contact telephone number.