Question: There are 15 balls in a jar. You take out 3 blue balls without putting them back inside, and now the probability of pulling out a blue ball is 1/3. How many blue balls were there in the beginning?\nOptions:\n(A) 12.\n(B) 9.\n(C) 8.\n(D) 7.\n(E) 6. Let's think first. Some random reasoning:
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7 = 3 blue balls + 12 / 3 The final answer: (D).
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