geometry homework

Question

In his collection, Marco has 5 large gold coins, 12 large silver coins, 15 small gold coins, and 3 small silver coins. If he randomly picks a coin, what is the probability that it is gold, given that the coin is small?

Answer 1

15/18=5/6

If you don't see it directly, remember that P(A|B)=P(A and B)/P(B)

Here A and B is "small and gold" and B is "small"