Найдем значение выражения при $$n = 81$$.
$$\frac{\frac{5}{\sqrt{n}}}{\frac{1}{\sqrt{n}} \cdot n \cdot 12} = \frac{5}{\sqrt{n}} \cdot \frac{\sqrt{n}}{n \cdot 12} = \frac{5}{n \cdot 12} = \frac{5}{81 \cdot 12} = \frac{5}{972}$$
$$\frac{5}{\sqrt{81}} / (\frac{1}{\sqrt{81}} * 81 * 12) = \frac{5}{9} / (\frac{1}{9} * 81 * 12) = \frac{5}{9} / (9 * 12) = \frac{5}{9} / 108 = \frac{5}{9} * \frac{1}{108} = \frac{5}{972}$$
$$\frac{5}{972} \approx 0.005144$$
Ответ: 5/972