The set of numbers of the form $\frac{a}{10^b} \subset \Bbb R$, $a, b \in \Bbb Z$ is not isolated

Question

If we want to show $\frac{a}{10^b}$, $a, b \in \Bbb Z$ is not isolated, then we have to show that $|\frac{a}{10^b} - \frac{c}{10^d}| < \epsilon$ for all $\epsilon > 0$, since isolated means that there is a neighborhood that doesn't contain more than one point of the form $\frac{a}{10^b}$, so if it's not isolated then every neighborhood about the point $\frac{a}{10^b}$ must contain at least one other point of the form $\frac{a}{10^b}$. Or is there another alternative approach to this?