Solution: The GCF of 5 and 78 is 1MethodsHow to find the GCF of 5 and 78 using Prime FactorizationOne way to find the GCF of 5 and 78 is to compare the prime factorization of each number. To find the prime factorization, you can follow the instructions for each number here:What are the Factors of 5?What are the Factors of 78?Here is the prime factorization of 5:515^151And this is the prime factorization of 78:21×31×1312^1 × 3^1 × 13^121×31×131When you compare the prime factorization of these two numbers, you can see that there are no matching prime factors. When this is the case, it means that there are no common factors between these two numbers. As a result, the GCF of 5 and 78 is 1.Thus, the GCF of 5 and 78 is: 1How to Find the GCF of 5 and 78 by Listing All Common FactorsThe first step to this method of finding the Greatest Common Factor of 5 and 78 is to find and list all the factors of each number. Again, you can see how this is done by looking at the “Factors of” articles that are linked to above.Let’s take a look at the factors for each of these numbers, 5 and 78:Factors of 5: 1, 5Factors of 78: 1, 2, 3, 6, 13, 26, 39, 78When you compare the two lists of factors, you can see that the only common factor is 1. So, in this case, the GCF of 5 and 78 is 1.Find the GCF of Other Number PairsWant more practice? Try some of these other GCF problems:What is the GCF of 8 and 10?What is the GCF of 48 and 128?What is the GCF of 105 and 73?What is the GCF of 14 and 9?What is the GCF of 86 and 56?