Given a matrix $A\in GL_n(\mathbb{Q})$. Can it be expressed as a product of two matrices $B,C$ with $B\in GL_n(\mathbb{Z}[1/p])$ and $C\in GL_{n}(\mathbb{Z}_{(p)})$, where $ \mathbb{Z_p}$ denotes the localization of $\mathbb{Z}$ at $(p)$ ?
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Yes, there exists such a decomposition. Multiplying $A$ by a suitable integer, we may assume that $A \in M_n(\mathbf{Z})$ and $\det(A) \neq 0$. By the theory of elementary divisors, we have $A=\gamma_1 D \gamma_2$ with $\gamma_1,\gamma_2 \in SL_n(\mathbf{Z})$ and $D$ is a diagonal matrix with nonzero integral entries. Now the result is true for $D$, and letting $D=M_1 M_2$ with $M_1 \in GL_n(\mathbf{Z}[1/p])$ and $M_2 \in GL_n(\mathbf{Z}_{(p)})$, we see that $B=\gamma_1 M_1$ and $C=M_2 \gamma_2$ work. 

