The prime factorization of 88 is $2^3\cdot 11$ and the prime factorization of 99 is $3^2\cdot 11$. The common factors of 88 and 99 are the prime factors that they share, specifically the factor of 11. Thus, the greatest common factor of 88 and 99 is $\boxed{11}$.
What is the Gcf of 87 and 93?
The prime factorization of 87 is $3\cdot 29$ and the prime factorization of 93 is $3\cdot 31$. The only prime factor that 87 and 93 share is 3. Thus, the greatest common factor of 87 and 93 is $\boxed{3}$.
What is the greatest common factor of 19 and 38?
The prime factorization of 19 is $19$ and the prime factorization of 38 is $2\cdot 19$. The only prime factor that 19 and 38 share is 19. Thus, the greatest common factor of 19 and 38 is $\boxed{19}$.
What is the greatest common factor of 88 and 99?
The prime factorization of 88 is $2^3\cdot 11$ and the prime factorization of 99 is $3^2\cdot 11$. The common factors of 88 and 99 are the prime factors that they share, specifically the factor of 11. Thus, the greatest common factor of 88 and 99 is $\boxed{11}$.
