Answer:
1. 6
2. 1
3. 5
Explanation:
You can find the GCF by finding the prime factorization of the numbers.
1. 12 and 18
12= 2*2*3
18=2*3*3
They both have 2 and 3 in common, so their GCF is 2*3 or 6.
2. 9 and 35
9= 3*3
35= 5*7
Although they don't have any prime numbers in common, all numbers have the factor one in common, so they're relatively prime but their GCF is 1.
3. 15 and 25
15 = 3*5
25= 5*5
They have one 5 in common so their GCF is 5.