G3.4 Let $x$ and $y$ be two positive numbers that are inversely proportional to each other. If $x$ is increased by $10 \%, y$ will be decreased by $d \%$, find the value of $d$.
$\begin{array}{l}x y=k, x_{1}=1.1 x \\ x_{1} y_{1}=x y \Rightarrow 1.1 x y_{1}=x y \\ y_{1}=\frac{10 y}{11}, \text { Percentage decrease }=\frac{y-\frac{10 y}{11}}{y} \times 100 \%=\frac{100}{11} \%, d=\frac{100}{11}\end{array}$