One way to find the GCF of 45 and 5 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 45:
And this is the prime factorization of 5:
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 45 and 5 by multiplying all the matching prime factors to get a GCF of 45 and 5 as 25:
Thus, the GCF of 45 and 5 is: 25