Let $z = \dfrac{k\sqrt{x}}{y}$, where $k$ is a non-zero constant.
Let $x_0$, $y_0$ and $z_0$ be the original values of $x$, $y$ and $z$ respectively.
Let $x_1$, $y_1$ and $z_1$ be the new values of $x$, $y$ and $z$ respectively.
$\begin{array}{rcl}
x_1 & = & x_0 \times ( 1-36\%) \\
x_1 & = & 0.64x_0
\end{array}$
$\begin{array}{rcl}
y_1 & = & y_0 \times (1+60\%) \\
y_1 & = & 1.6y_0
\end{array}$
Therefore, the percentage change of $z$
$\begin{array}{cl}
= & \dfrac{z_1 – z_0}{z_0} \times 100\% \\
= & \dfrac{\frac{k\sqrt{x_1}}{y_1} – \frac{k\sqrt{x_0}}{y_0}}{\frac{k\sqrt{x_0}}{y_0}} \times 100 \% \\
= & \dfrac{\frac{k\sqrt{0.64x_0}}{1.6y_0} – \frac{k\sqrt{x_0}}{y_0}}{\frac{k\sqrt{x_0}}{y_0}} \times 100 \% \\
= & \dfrac{\frac{k\sqrt{x_0}}{y_0} \left( \frac{0.8}{1.6} – 1 \right) }{\frac{k\sqrt{x_0}}{y_0}} \times 100 \% \\
= & -50 \%
\end{array}$
Therefore, $z$ is decreased by $50\%$.
