Discussion
A box contains 2 white balls, 3 black balls and 4 red balls. In how many ways can 3 balls be drawn from the box, if at least one black ball is to be included in the draw?
Answer: C
The box holds \( 2 + 3 + 4 = 9 \) balls, six of them not black.
\[ \text{total} = {}^{9}C_{3} = 84 \]
\[ \text{no black} = {}^{6}C_{3} = 20 \]
\[ 84 - 20 = 64 \]
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