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    Question

    A bag contains 8 white and some black balls. If the

    probability of drawing a black ball from the bag is twice that of drawing a white ball, find the number of black balls in the bag.
    A 15 Correct Answer Incorrect Answer
    B 10 Correct Answer Incorrect Answer
    C 17 Correct Answer Incorrect Answer
    D 16 Correct Answer Incorrect Answer

    Solution

    Number of white balls = 8 Let x be the number of black balls. Total number of balls in the bag = 8 + x Also, the probability of drawing a black ball from the bag is twice that of drawing a white ball. ⇒ x/(8 + x) = 2 [8/(8 + x)] ⇒ x = 2 × 8 = 16 Hence, the number of black balls in the bag = 16

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