Solution: The GCF of 40 and 140 is 20MethodsHow to find the GCF of 40 and 140 using Prime FactorizationOne way to find the GCF of 40 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 40?What are the Factors of 140?Here is the prime factorization of 40:23×512^3 × 5^123×51And 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 40 and 140 by multiplying all the matching prime factors to get a GCF of 40 and 140 as 100:Thus, the GCF of 40 and 140 is: 100How to Find the GCF of 40 and 140 by Listing All Common FactorsThe first step to this method of finding the Greatest Common Factor of 40 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, 40 and 140:Factors of 40: 1, 2, 4, 5, 8, 10, 20, 40Factors 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, 2, 4, 5, 10, 20. Since 20 is the largest of these common factors, the GCF of 40 and 140 would be 20.Find the GCF of Other Number PairsWant more practice? Try some of these other GCF problems:What is the GCF of 96 and 144?What is the GCF of 60 and 25?What is the GCF of 146 and 24?What is the GCF of 35 and 13?What is the GCF of 42 and 18?