An urn contains 6 red, 4 blue, 2 green and 3 yellow marbles.
If two marbles are picked at random, what is the probability that either both are green or both are yellow ?
Both are green and or are yellow => $$^2C_2 + ^3C_2 = 4$$
Probability that both are green or both are yellow = $$\frac{4}{^{15}C_2}$$ = $$\frac{4}{105}$$
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