There are 7 red and 5 yellow fish in an aquarium. Three fish are randomly...

There are 7 red and 5 yellow fish in an aquarium. Three fish are randomly caught in a net. Find the probability that the fish were:
a) All red
b) Not all of the same color.

I have solved this question using the method for dependent events as follows:
a) $\frac{7}{12}\cdot \frac{6}{11}\cdot \frac{5}{10}=\frac{210}{1320}$
b) $1-(\frac{7}{12}\cdot \frac{6}{11}\cdot \frac{5}{10}+\frac{5}{12}\cdot \frac{4}{11}\cdot \frac{3}{10})=\frac{1170}{1320}$
Is it possible to use combinations to solve this question? If yes, how?