Answer: 5
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Step-by-step explanation:
Find the prime factorization of each value. A factor tree may help.
10 = 2*5
30 = 2*3*5
45 = 3*3*5
We see that '5' is found in each of the factorizations. This is the only factor that shows up in all three values, and it only shows up one time. So that's why 5 is the GCF.