Question 214732
In a box there are 7 balls, of which 3 are red and 4 are white. Three balls will be withdrawn at random. Find the probability that at least one ball will be red. 
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P(at least one ball is red) = 1 - P(no ball is red)
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P(at least one) = 1 - [4C3/7C3] = 1 - 4/35 = 31/35
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Cheers,
Stan H.