$$y=\frac{x}{\sqrt{x}+1}$$

(正答率 44%)

$$\begin{eqnarray*} y'&=& \frac{x'(\sqrt{x}+1)-x\times(\sqrt{x}+1)}{(\sqrt{x}+1)^2... ...{x}}{2(\sqrt{x}+1)^2}\\ &=&\frac{\sqrt{x}+2}{2(\sqrt{x}+1)^2} \end{eqnarray*}$$