a) \(\frac{a}{b} : \frac{m}{n} = \frac{a}{b} \cdot \frac{n}{m} = \frac{a \cdot n}{b \cdot m}\)
б) \(\frac{s}{t} : c = \frac{s}{t} : \frac{c}{1} = \frac{s}{t} \cdot \frac{1}{c} = \frac{s \cdot 1}{t \cdot c} = \frac{s}{t \cdot c}\)
в) \(d : \frac{a}{m} = \frac{d}{1} : \frac{a}{m} = \frac{d}{1} \cdot \frac{m}{a} = \frac{d \cdot m}{1 \cdot a} = \frac{d \cdot m}{a}\)