Question
A bowl contains 9 blue balls, 7 white, and 5 black
balls. If 2 balls are drawn in one go, then the probability of exactly one ball being white is:Solution
In total, we have 9+7+5=21 balls. We have drawn 2 balls; we can draw them in 21C2 ways = 21! ÷ (19! ×2!) = 210 ways. In those two balls, we need one to be a white ball, so we can include that in 7C1 ways = 7 ways. The remaining ball may be any color ball but not white, so we select other balls in 14C1 ways= 14 ways. Probability= (7×14)/210 =7/15.
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