\[\boxed{\mathbf{2.453}}\]
Пояснение.
Решение.
\[\textbf{а)}\ \frac{a}{b}\ :\frac{m}{n} = \frac{a}{b} \cdot \frac{n}{m} = \frac{\text{an}}{\text{bm}}\]
\[\textbf{б)}\ \frac{s}{t}\ :c = \frac{s}{t} \cdot \frac{1}{c} = \frac{s}{\text{tc}}\]
\[\textbf{в)}\ d\ :\frac{a}{m} = d \cdot \frac{m}{a} = \frac{\text{dm}}{a}\]