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    Question

    A sack contains 'r' silver balls and 12 gold balls. If

    the probability of getting a silver ball is 1/4, then find the probability of getting different coloured balls when two balls are drawn randomly from the sack.
    A (1/5 Correct Answer Incorrect Answer
    B (1/4 Correct Answer Incorrect Answer
    C (2/5 Correct Answer Incorrect Answer
    D (1/2 Correct Answer Incorrect Answer
    E (3/5 Correct Answer Incorrect Answer

    Solution

    Total number of balls in the sack = r + 12
    So, r/(r + 12) = 1/4
    Or, 4r = r + 12
    Or, 3r = 12
    So, r = 4
    Total balls = 4 + 12 = 16
    Desired Probability = (4C1 × 12C1)/16C2 = (4 × 12)/(16 × 15/2) = 48/120 = 2/5

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