a) $$\frac{5}{12} \div \frac{1}{4} = \frac{5}{12} \cdot \frac{4}{1} = \frac{5 \cdot 4}{12 \cdot 1} = \frac{5 \cdot 1}{3 \cdot 1} = \frac{5}{3} = 1 \frac{2}{3}$$
Ответ: $$1 \frac{2}{3}$$
b) $$\frac{7}{10} \div \frac{2}{5} = \frac{7}{10} \cdot \frac{5}{2} = \frac{7 \cdot 5}{10 \cdot 2} = \frac{7 \cdot 1}{2 \cdot 2} = \frac{7}{4} = 1 \frac{3}{4}$$
Ответ: $$1 \frac{3}{4}$$