An urn contains 6 red, 4 blue, 2 green and 3 yellow marbles.
If four marbles are picked at random, what is the probability that at least one is blue ?
Probability that at least 1 is blue => 1 - (probability that none is blue) => 1 - $$(\frac{^{11}C_4}{^{15}C_4})$$ = $$\frac{69}{91}$$
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