109.Second Black on the Third Draw
★★★combinatoricsSIG
A bag holds 30 balls: 10 black, 5 orange, 10 green and 5 blue. Balls are drawn without replacement. What is the probability that the second black ball appears on exactly the third draw?
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The third draw must be black and exactly one of the first two must be black. Chain the conditional probabilities for both orderings.
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