SOLUTION: A bag contains 7 white marbles and 9 blue marbles. Two marbles are chosen without replacement. Find the probability of selecting a blue marble on the second draw given that the fir
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Question 1098361: A bag contains 7 white marbles and 9 blue marbles. Two marbles are chosen without replacement. Find the probability of selecting a blue marble on the second draw given that the first marble drawn was white?
By using a probability tree, I got the answer 21/80, but apparently that's not right, please help! Answer by rothauserc(4718) (Show Source):
You can put this solution on YOUR website! This is a conditional probability
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there are 16 marbles in the bag
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now a white marble was selected first so for the second selection there are only 15 marbles in the bag and 9 of them are blue
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Probability of selecting a blue marble given a white ball was selected first = 9/15 = 3/5
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your calculation gave you the probability of choosing a white ball first AND a blue ball for the second selection
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