EDEXCEL GCSE FOUNDATION MATHS - What are Prime Numbers

Edexcel GCSE Foundation Maths - What are Prime Numbers?

What are Prime Numbers?

A prime number is a whole number greater than 1 that has only two factors (divisors): 1 and itself.

Examples of Prime Numbers:

• 2 - Only divisible by 1 and 2
• 3 - Only divisible by 1 and 3
• 5 - Only divisible by 1 and 5
• 7 - Only divisible by 1 and 7
• 11 - Only divisible by 1 and 11

Examples of Numbers that are NOT Prime Numbers:

• 1 - Only has one factor (itself)
• 4 - Divisible by 1, 2, and 4
• 6 - Divisible by 1, 2, 3, and 6
• 9 - Divisible by 1, 3, and 9

Key Points:

• 1 is NOT a prime number.
• 2 is the ONLY even prime number.
• There are infinitely many prime numbers.

How to Determine if a Number is Prime:

1. Check if the number is greater than 1.
2. Divide the number by all the numbers from 2 up to the square root of the number.
3. If the number is only divisible by 1 and itself, then it is a prime number.

Example:

Is 17 a prime number?

1. 17 is greater than 1.
2. The square root of 17 is approximately 4.12.
3. Divide 17 by all the numbers from 2 to 4 (2, 3, and 4). 17 is not divisible by any of these numbers.
4. Therefore, 17 is a prime number.

Practice:

Determine which of the following numbers are prime numbers:

• 13
• 21
• 29
• 36

Answers:

• 13 - Prime
• 21 - Not prime
• 29 - Prime
• 36 - Not prime