A bag contains 2 blue marbles, and 3 black marbles. If 3 marbles are selected, what is the probability of picking 3 black marbles?

There are LaTeX: \displaystyle C(5,3)=10 to select 3 marbles. There are LaTeX: \displaystyle 1 ways to select 3 black from 3 black. This gives the probability LaTeX: \displaystyle \frac{1}{10}