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    Question

    A bag has x blue balls and 4 yellow balls. If the

    probability of picking a blue ball is 3/5, find the probability that two balls drawn at once are of different colours.
    A 2/13 Correct Answer Incorrect Answer
    B 4/15 Correct Answer Incorrect Answer
    C 8/15 Correct Answer Incorrect Answer
    D 21/13 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Total number of balls = x + 4 So, x / (x + 4) = 3/5 ⇒ 5x = 3x + 12 ⇒ 2x = 12 ⇒ x = 6 Desired Probability = (⁶C₁ × ⁴C₁) / ¹⁰C₂ = (6 × 4) / (10 × 9 / 2) = 24 / 45 = 8/15

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