One way to find the GCF of 7 and 91 is to compare the prime factorization of each number. To find the prime factorization, you can follow the instructions for each number here:
Here is the prime factorization of 7:
And this is the prime factorization of 91:
When 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 7 and 91 by multiplying all the matching prime factors to get a GCF of 7 and 91 as 49:
Thus, the GCF of 7 and 91 is: 49