# Multinomial Distribution

An urn contains 1 blue, 1 green and 1 yellow ball. With replacement, we draw out a ball 7 times and record down the color seen. What is the probability that we see an equal number of blue and green balls?

The answer can be written as $$\dfrac{a}{b}$$ with $$a$$ and $$b$$ coprime positive integers. Submit $$a+b$$.

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