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Prime numbers are positive integers that have only two factors: 1 and itself.
For example, 2, 3, 5, 7 are all prime numbers.
Composite numbers are numbers that has two or more factors.
For example, 4, 6, 8, 10 are all composite numbers.
Poor old number 1 is neither a prime nor a composite number while the number 2 is the only even prime number.
Let's do the below questions together to make sure we understand. Start with writing down the factors of each number then review the descriptions we have written down for prime and composite numbers. If it only has two factors which are the number 1 and itself it is prime, otherwise it is composite.
Finding prime factors
A prime factor is simply the factors of a number that are prime.
Let's have a go at finding the prime factors of 20.
Step 1 - find the entire set of factors.
The factors of 20 include 1, 2, 4, 5, 10, 20
1 x 20 = 20
2 x 10 = 20
4 x 5 = 20
Step 2 - determine which of these factors are prime (the numbers that only have two factors being 1 and itself).
The factors 2 and 5 are prime factors of 20.
It's your turn!
Please start completing the questions on your ticksheet from 11B, remember to tick them off as you go.
Hint - we have already started question 7 so you can tick these off now.
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