Maths Unit 7 - Multiples, Factors, Primes & Negatives A prime number is a number which only has two factors – itself and 1. The first 10 prime numbers are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29 A common mistake is that people think 1 is a prime number. The only way to make 1 is by doing 1 x 1 , so the number 1 only has one factor NOT two factors, therefore it is NOT prime. Examples Is 11 prime? - 1 x 11 Yes it’s prime Is 12 prime? – 1 x 12, 2 x 6, 3 x 4 No it’s not prime A multiple is a number which can be divided by another number without a remainder. For example: 15, 20 100, 150 are multiples of 5 because they can be divided by 5 and have no remainder Factors An exact divisor of a number is called a factor. Factors can be written in pairs to help find all the factors of a given number. E.g. Factors of 12 can be written like this….. Prime Factorisation All numbers can be written as a product of their primes i.e. each number can be made by multiply prime numbers together. A factor tree helps you find which prime numbers multiply to make a given number. Key words and definitions Multiple - a number which can be divided by another number without a remainder. Divisor – the number you divide by. Factor - An exact divisor of a number. Prime - a number which only has two factors Product – the result of multiplying to numbers together Prime Factorisation – a list of prime numbers which multiply together to create another number E.g. The prime factors of 75 are 3, 5 and 5. It is said that 75 is a product of 3 x 5 2 .