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


Prime Numbers

If a number has only two different factors, 1 and itself, then the number is said to be a prime number.

The factors of 7 are 1 and 7.
7 is a prime number since it has only two different factors.


Note:

The only factor of 1 is 1.

But 1 is not a prime number since it does not have two different factors.

 
2, 3, 5, 7 and 11 are numbers that have two factors.
 
Therefore, 2, 3, 5, 7 and 11 are prime numbers.


Composite Numbers

A number that has more than two factors is called a composite number.
 
The factors of 14 are 1, 2, 7 and 14.
So, 14 is a composite number as it has more than two factors.
 
Note:

1 is considered neither a prime number nor a composite number.


Example 10

State which of the following numbers are a prime:

a.  46
b.  19

Solution:

a.  46 is not a prime because 46 = 2 × 23.
b.  19 is a prime since it has only two different factors, 1 and 19.


Example 11

Express 210 as a product of prime numbers.

Solution:

210 expressed as the product of prime factors is 2 × 3 × 5 × 7.


Note:

We try the prime numbers in order of their magnitude.


Example 12

Express 90 as a product of prime numbers.

Solution:

90 expressed as the product of prime factors is 2 × 3 squared × 5.

Alternatively, we can use a factor tree to express 90 as a product of prime numbers as illustrated below.

A factor tree can be used to identity prime numbers.

So 90 expressed as the product of prime factors is 2 × 3 squared × 5.


Key Terms

prime number, composite numbers, factor tree


| 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 | Tutor Software | Maths Software Platform | Trial Maths Software |
| Feedback | About mathsteacher.com.au | Terms and Conditions | Our Policies | Links | Contact |

Copyright © 2000-2022 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.