<PRE><B>Question 667861</B>
Two marbles are drawn without replacement from a jar with 4 black and 3 white marbles.  
What is the probability that both marbles are white?
Ans: 3C2/7C2 = 3/21 = 1/7
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That the second marble drawn is white, given that the first is black?
Ans: P(w|b) = 3/6 = 1/2
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  That the first marble is black and the second marble is white?  
Ans: P(b and w) = (4/7)(3/6) = 2/7
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That at least one of the marbles is black?
Ans: P(condition) = 1 - P(2 white) = 1 - 3C2/7C2 = 1-[3/21] = 6/7
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Cheers,
Stan H.
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