An urn contains 5 red marbles, 4 black marbles and 3 white marbles. Then the number of ways in which 4 marbles can be drawn so that at most three of them are red is
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Solution
Number of ways to select at most 3 red balls =p(0 red ball)+p(1 red ball)+P(2 red balls)+P(3 red balls) =7C4+5C1×7C3+5C2×7C2+5C3×7C1 =35+175+210+70=490