20) 5 1/7:1,2=

20) $$5 \frac{1}{7} : 1,2 = \frac{36}{7} : \frac{12}{10} = \frac{36}{7} \cdot \frac{10}{12} = \frac{36 \cdot 10}{7 \cdot 12} = \frac{360}{84} = \frac{30}{7} = 4 \frac{2}{7}$$

Ответ: 4 2/7