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There are x red marbles, y blue marbles, and z yellow marbles in a sack. Three marbles are chosen at random, without replacements. If x, y, and z are all at least equal to 3, then which of the following must be true? Indicate all possible values.

A.The probability of drawing exactly 3 red marbles is$$(x/(x+y+z))((x-1)/(x+y+z-1))((x-2)/(x+y+z-2))$$
B.The probability of drawing at least 1 red marble is$$1-((y+z)/(x+y+z))((y+z-1)/(x+y+z-1))((y+z-2)/(x+y+z-2))$$
C.The probability of drawing exactly 3 blue marbles is$$(y/(x+y+z))((y-z)/(x+y+z-1))((y+z)/(x+y+z-2))$$

A,B显示答案

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