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Level pending

If from each of the three boxes containing 3 white and 1 black, 2 white and 2 black, 1 white and 3 black balls, one ball is drawn at random, then the probability that 2 white and 1 black ball will be drawn is given by $$\frac{a}{b}$$ where $$a$$ and $$b$$ are relatively prime. then $$a + b$$ is given by

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