Solution: The GCF of 15 and 4 is 1MethodsHow to find the GCF of 15 and 4 using Prime FactorizationOne way to find the GCF of 15 and 4 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 15?What are the Factors of 4?Here is the prime factorization of 15:31×513^1 × 5^131×51And this is the prime factorization of 4:222^222When 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 15 and 4 is 1.Thus, the GCF of 15 and 4 is: 1How to Find the GCF of 15 and 4 by Listing All Common FactorsThe first step to this method of finding the Greatest Common Factor of 15 and 4 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, 15 and 4:Factors of 15: 1, 3, 5, 15Factors of 4: 1, 2, 4When you compare the two lists of factors, you can see that the only common factor is 1. So, in this case, the GCF of 15 and 4 is 1.Find the GCF of Other Number PairsWant more practice? Try some of these other GCF problems:What is the GCF of 12 and 110?What is the GCF of 78 and 127?What is the GCF of 120 and 72?What is the GCF of 60 and 80?What is the GCF of 49 and 62?