\textbf{123-} What is the mean value (average) of the function $f(x) = \dfrac{2x-1}{\sqrt{x}}$ on the interval $[1, 4]$?
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\hspace{1cm} (1) $\dfrac{17}{9}$ \hspace{2.5cm} (2) $\dfrac{7}{3}$ \hspace{2.5cm} (3) $\dfrac{22}{9}$ \hspace{2.5cm} (4) $\dfrac{8}{3}$
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