Year 7 Interactive Maths - Second Edition

Prime Numbers

7 is a prime number since it has only two different factors.

Note:

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

Composite Numbers

A number that has more than two factors is called a composite number.

 

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:

Note:

We try the prime numbers in order of their magnitude.

Example 12

Express 90 as a product of prime numbers.

Solution:

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

Key Terms

prime number, composite numbers, factor tree