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    Question

    A bag contains 20 white and some black balls. If the

    probability of drawing a black ball from the bag is 2.5 times that of drawing a white ball, find the number of black balls in the bag.
    A 38 Correct Answer Incorrect Answer
    B 50 Correct Answer Incorrect Answer
    C 36 Correct Answer Incorrect Answer
    D 37 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Given, Number of white balls = 20 Let x be the number of black balls. Total number of balls in the bag = 20 + x Also, the probability of drawing a black ball from the bag is 2.5 times that of drawing a white ball. ⇒ x/(20 + x) = 2.5[20/(20 + x)] ⇒ x = 50 Hence, the number of black balls in the bag = 50.

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