# 2 for the cost of 1

Let $$A$$ be the constant term in the expansion of $${\left(x+x^2+\dfrac{1}{x}+\dfrac{1}{x^2}\right)}^{15}$$.

Let $$B$$ be the value of $$\displaystyle \sum _{ r=0 }^{ 5 }{ \begin{pmatrix} 15 \\ r+5 \end{pmatrix} } \begin{pmatrix} 15 \\ 3r \end{pmatrix}$$.

Find the value of $$\frac {2 A }{ B }$$.

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