# Multinomial Distribution

**Discrete Mathematics**Level 3

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 \( a+b\).