GWD1-37,概率

请教解题思路

Q37:

A jar contains 16 marbles, of which 4 are red, 3 are blue, and the rest are yellow.  If 2 marbles are to be selected at random from the jar, one at a time without being replaced, what is the probability that the first marble selected will be red and the second marble selected will be blue?

A.     3/64

B.      1/20

C.      1/16

D.     1/12

E.      1/8

Answer: B