Question 504726: An urn contains 4 red, 5 white, and 4 blue marbles. In how many ways can three marbles be selected so that at least one of them is blue?
I've tried C(4,1) x C(9,2) + C(4,2) x C(9,1) = 198. I'm getting an "incorrect" response when I click submit.
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! An urn contains 4 red, 5 white, and 4 blue marbles. In how many ways can three marbles be selected so that at least one of them is blue?
I've tried C(4,1) x C(9,2) + C(4,2) x C(9,1) = 198. I'm getting an "incorrect" response when I click submit.
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#(at least one blue) = #(all sets of 3) - #(no blue)
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#(at least one blue) = 13C3 - 9C3
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#(at least one blue) = 286-84 = 202 ways
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Cheers,
Stan H.
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