а) \(\frac{a}{b}:\frac{m}{n} = \frac{a}{b} \cdot \frac{n}{m} = \frac{a \cdot n}{b \cdot m} = \frac{an}{bm}\)
б) \(\frac{s}{t}:c = \frac{s}{t}:\frac{c}{1} = \frac{s}{t} \cdot \frac{1}{c} = \frac{s \cdot 1}{t \cdot c} = \frac{s}{tc}\)
Ответ: а) \(\frac{an}{bm}\); б) \(\frac{s}{tc}\)