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    Question

    Among a set of 4 black balls and 3 white balls, how

    many selections of 3 balls can be made such that at least 2 of them are black balls?
    A 156 ways Correct Answer Incorrect Answer
    B 22 ways Correct Answer Incorrect Answer
    C 188 ways Correct Answer Incorrect Answer
    D 180 ways Correct Answer Incorrect Answer
    E 120 ways Correct Answer Incorrect Answer

    Solution

    Selecting at least 2 black balls from a set of 4 black balls in total selection of 3 balls can be 2 black and 1 white balls 3 black and 0 white balls Therefore, our solution expression looks 4C2 × 3C1 + 4C3 × 3C0 6 X 3 + 4 X 1 = 18 + 4 = 22 ways

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