Question
Among a set of 6 black balls and 3 white balls, how many
selections of 5 balls can be made such that at least 3 of them are black balls?Solution
Selecting at least 3 black balls from a set of 6 black balls in total selection of 5 balls can be 3 black and 2 white balls 4 black and 1 white balls 5 black and 0 white balls Therefore, our solution expression looks 6C3 × 3C2 + 6C4 × 3C1 + 6C5 × 3C0 = 20 × 3 + 15 × 3 + 6 × 1 = 60 + 45 + 6 = 111 ways
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