г) 5/7 * 3/4 + 3/4 * 3/7; д) 1 1/4 * 4/21 - 1 1/4 * 2/7; e) 14,2 * 5/9 - 12,4 * 5/9;

Ответ: г) 3/4; д) 5/84; е) 1

г) \[\frac{5}{7} \cdot \frac{3}{4} + \frac{3}{4} \cdot \frac{3}{7} = \frac{15}{28} + \frac{9}{28} = \frac{15+9}{28} = \frac{24}{28} = \frac{6}{7}\]

д) \[1\frac{1}{4} \cdot \frac{4}{21} - 1\frac{1}{4} \cdot \frac{2}{7} = \frac{5}{4} \cdot \frac{4}{21} - \frac{5}{4} \cdot \frac{2}{7} = \frac{20}{84} - \frac{10}{28} = \frac{20}{84} - \frac{30}{84} = \frac{20-30}{84} = -\frac{10}{84} = -\frac{5}{42}\]

е) \[14.2 \cdot \frac{5}{9} - 12.4 \cdot \frac{5}{9} = \frac{5}{9} \cdot (14.2 - 12.4) = \frac{5}{9} \cdot 1.8 = \frac{5}{9} \cdot \frac{18}{10} = \frac{5 \cdot 18}{9 \cdot 10} = \frac{90}{90} = 1\]

Ответ: г) 3/4; д) 5/84; е) 1