Page 10 - Math Smart - 7

A number that has only two factors is called a prime number. The factors of
a prime number are always the number 1, and the number itself. The prime
numbers in Investigate! on the previous page are: 13 and 53. The number 13 has
why is the number
only two factors: 1 and 13. The number 53 has only two factors: 1 and 53.
1 neither prime nor
composite? A composite number has more than two factors. As you saw in Investigate! on
the previous page, the numbers 100, 8, 30, 24 and 18 are composite numbers.
All of these numbers have more than two factors. The number 1 is neither prime
nor composite.

Check My

Understanding

O Circle the prime numbers.

8 12 27 7 36 18 11 19 9

Q Match the terms to their descriptions.

1. Prime number The result obtained when two or more
Amazing numbers are multiplied
Mathematician 2. Factor A number that has exactly two factors:
1 and itself

3. Product A number which divides into another
number exactly without leaving a remainder

@ Put a tick in the correct column.

Number Prime number Composite number

2
The sieve of
8
Eratosthenes can be
13
used to find prime
numbers. 25
Find out more about 70
Eratosthenes.

SMH
The sieve of Eratosthenes
Eratosthenes was a Greek mathematician. He developed a method of finding
prime numbers up to 100 by eliminating or sieving out all composite numbers,
and the number 1. This is called the sieve of Eratosthenes.

Factors, Multiples and Primes