Grade FG Prime numbers Identifying a prime number

Grade F/G Prime numbers Identifying a prime number and finding prime factors of numbers If you have any questions regarding these resources or come across any errors, please contact helpful-report@pixl. org. uk

Key vocabulary Prime Product Factor Multiple HCF (Highest common factor) LCM (Lowest common multiple)

How to identify a prime number Find all the prime numbers between 1 and 100 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 Remove all multiples of 2 except 2 Remove all multiples of 3 except 3 Remove all multiples of 5 except 5 Remove all multiples of 7 except 7 Remove number 1 All numbers remaining are prime numbers A prime number is a number that has two factors 1 and itself.

How to identify a prime number List all the prime numbers between 50 and 60 To identify a prime number we know that it only has two factors 1 and itself 50 51 52 53 54 55 56 57 58 59 60 Even numbers are multiples of 2 therefore they can not be prime Identify any number that is a multiple of 3 Identify any number that is a multiple of 5 Identify any number that is a multiple of 7 53 and 59 are the only prime numbers between 50 and 60

Product of prime numbers 2) Write 120 as a product of its prime numbers. Is 60 a prime number? No, so repeat the process 120 60 30 6 3 2 5 2 2 You can start by using any factor pair of 120 e. g. 60 x 2 2 is a prime number which can be circled A product is the result of multiplying

Identifying prime numbers. Now you try… a) Is 49 a prime number? Explain your answer b) Complete the list of prime numbers 2 , 3 , __ , 11 , __, 17 , 19 c) Write down all the prime numbers between 10 and 30 d) Identify all the prime numbers in the list 15 , 3, 29, 35, 51, 61, 19 e) Give an example of two prime numbers between 1 and 10 that add together to make a square number.

Identifying prime numbers-Now you try… a) Is 49 a prime number? Explain your answer 49 is not prime because it has more than two factors and is a multiple of 7 b) Complete the list of prime numbers 22, , 33, , __ , 11 , __, , 19 5 , , 7__ , 11 , 13, 1717 , 19 c) Write down all the prime numbers between 10 and 30 11, 13, 17, 19, 23, 29, 31, 37 d) Identify all the prime numbers in the list 15 , 3, 29, 35, 51, 61, 19 3, 19, 29, 61 e) Give an example of two prime numbers between 1 and 10 that add together to make a square number. 2+2= 4 7+2=9

Product of prime numbers. Now you try…. a) Write 48 as a product of its prime factors. b) Write 72 as product of its prime factors.

Product of prime numbers- Now you try…. a) Write 48 as a product of its prime factors. b) Write 72 as product of its prime factors.

Problem solving and reasoning Question 1 Sally is thinking of a prime number between 30 and 40. If the digits of the number are added together to make 10 what is the number she is thinking of?

Problem solving and reasoning Question 1 Sally is thinking of a prime number between 30 and 40. If the digits of the number are added together to make 10 what is the number she is thinking of? First eliminate all multiples of 2, 3, 5 and 7 to identify all the prime numbers between 30 and 40. 31 and 37 are both prime Out of the two which digits add up to make 10? 3+1= 4 3+7=10 37 must be the number we are looking for as it is prime and adds together to make 10.