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?
~$\frac{3}{64}$~
~$\frac{1}{20}$~
~$\frac{1}{16}$~
~$\frac{1}{12}$~
~$\frac{1}{8}$~
without replaced... 不放回 所以分母不能是C16 2 (一次性从16个里面拿两个)
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