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A bag contains 5 red marbles and 3 black marbles. Three marbles are drawn one by one without replacement. What is the probability that at least one of the three marbles drawn be black, if the first marble is red?

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Bag contains 5 red marbles and 3 black marbles, 
For atleast one of the three marbles drawn be black, if the first marble is red,
then the following situations are possible 
Event E1 = Second marble is black and third is red 
Event E2 = Second marble is black and third is also black (E2)
Event E3 = Second marble is red and third is black (E3)
Let Event Ri = drawing red marble in ith draw 
Event Bi = drawing black marble in ith draw 

   

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