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How do you use prime factorization to find the GCF or LCM of two whole numbers? For example, how do you use prime factors to find the GCF and LCM of 8 and 30? In this lesson you will learn how to find the GCF and LCM of two whole numbers by using their prime factors. Let’s Review Prime numbers have only two factors, one and themselves. 7 is a prime number. 7 x 1 = 7 The first few prime numbers are 2, 3, 5, 7, 11, 13, 17… Composite numbers have more than two factors. 10 is a composite number. 1 x 10 = 10 2 x 5 = 10 Let’s Review factor tree 40 2 x 20 2 x 10 2x5 The first few prime numbers are 2, 3, 5, 7, 11, 13, 17… Prime factorization is finding a string of prime numbers that when multiplied result in your original number. 40 = 2 x 2 x 2 x 5 All composite numbers can be written as a string of prime factors. A Common Misunderstanding Confusing factors with multiples Find the factors of 25. 1, 5, 25 25, 50, 75… A Common Misunderstanding Remembering to find only prime factors for a number when using prime factorization. The prime factors of 20 are 2 x 10. Core Lesson How do you use prime factorization to find the GCF and LCM of 8 and 30? factor tree 8= 2 x 2 x 2 30 = 2 x 3 x 5 2x4 2x2 2 x 15 3x5 Venn Diagram Core Lesson The GCF of 8 and 30 is 2. 8= 2 x 2 x 2 2 LCM 2 GCF 2 30 = 2 x 3 x 5 3 5 2 x 2 x 2 x 3 x 5 = 120 The LCM of 8 and 30 is 120. Core Lesson What is the GCF and LCM of 18 and 27? 18 = 2 x 3 x 3 2x9 3x3 27 = 3 x 3 x 3 3x9 3x3 Core Lesson Venn Diagram GCF 3 x 3 = 9 The GCF of 18 and 27 is 9. 27 = 3 x 3 x 3 18 = 2 x 3 x 3 2 LCM 3 3 3 2 x 3 x 3 x 3 = 54 The LCM of 8 and 30 is 54. In this lesson you have learned how to find the GCF and LCM of two whole numbers by using their prime factors.