# Prime Numbers

*Keywords:*

AO elaboration and other teaching resources

Solve problems by finding the prime factors of numbers.

Number Framework Stage 8

#### Using Materials

Problem: “Gerry builds rectangles out of 6 square tiles. Find all the ways of building rectangles with these tiles.”

*(Answer: )*

“Repeat for 7 tiles.”

*(Answer: )*

Discuss why 7 is called a prime number and 6 is not.

*(Answer: There is only one way of building 7 namely 7 tiles in a single row. Whereas **6 can also be built as 2 rows of 3.)*

Examples: By building rectangles out of tiles determine which of these numbers are prime and which are not: 5 8 11 9 15 13 16.

#### Understanding Number Properties:

Explain why 2 is the only even prime number.

#### Using Number Properties

Problem: “7 has factors 1 and 7, and 7 is a prime number. 6 has factors 1, 2, 3, and 6, and 6 is *not *a prime number. Complete this general rule: If we look at all the factors of a number, we know when it is a prime number if..".