1. EASY

What is the greatest common factor of 12 and 9?

 
2. MEDIUM

What is the greatest common factor of 25 and 75?

 
3. MEDIUM

What is the greatest common factor of 99 and 45?

 
4. HARD

What is the greatest common factor of 6 and 37?

 
5. HARD

Greatest common factor of 91 and 65?