Solution: The GCF of 55 and 140 is 5MethodsHow to find the GCF of 55 and 140 using Prime FactorizationOne way to find the GCF of 55 and 140 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 55?What are the Factors of 140?Here is the prime factorization of 55:51×1115^1 × 11^151×111And this is the prime factorization of 140:22×51×712^2 × 5^1 × 7^122×51×71When you compare the prime factorization of these two numbers, you can see that there are matching prime factors. You can now find the Greatest Common Factor of 55 and 140 by multiplying all the matching prime factors to get a GCF of 55 and 140 as 25:Thus, the GCF of 55 and 140 is: 25How to Find the GCF of 55 and 140 by Listing All Common FactorsThe first step to this method of finding the Greatest Common Factor of 55 and 140 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, 55 and 140:Factors of 55: 1, 5, 11, 55Factors of 140: 1, 2, 4, 5, 7, 10, 14, 20, 28, 35, 70, 140When you compare the two lists of factors, you can see that the common factor(s) are 1, 5. Since 5 is the largest of these common factors, the GCF of 55 and 140 would be 5.Find the GCF of Other Number PairsWant more practice? Try some of these other GCF problems:What is the GCF of 150 and 100?What is the GCF of 7 and 145?What is the GCF of 76 and 60?What is the GCF of 88 and 27?What is the GCF of 9 and 18?