# Summation Summation Summation

Algebra Level 4

Given $$x_k, y_k, z_k > 0$$ for all $$k$$ satisfy the three summations:

$\begin{eqnarray} \displaystyle \sum_{k=1}^{2015} x_k & = & 50 \\ \displaystyle \sum_{k=1}^{2015} y_k & = & 169 \\ \displaystyle \sum_{k=1}^{2015} z_k & = & 961 \\ \end{eqnarray}$

What is the minimum value of $$\displaystyle \sum_{k=1}^{2015} \left ( x_k y_k z_k \right )$$?

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