г) 5/7 * 3/4 + 3/4; д) 1 1/4 * 4/21 - 1 1/4 * 1/7; е) 14.2 * 5/9 - 12.4 * 5/9;

г)

• \[ \frac{5}{7} \times \frac{3}{4} + \frac{3}{4} = \frac{15}{28} + \frac{3}{4} = \frac{15}{28} + \frac{21}{28} = \frac{36}{28} = \frac{9}{7} \]

д)

• \[ 1\frac{1}{4} \times \frac{4}{21} - 1\frac{1}{4} \times \frac{1}{7} = \frac{5}{4} \times \frac{4}{21} - \frac{5}{4} \times \frac{1}{7} = \frac{5}{4} \times \left( \frac{4}{21} - \frac{1}{7} \right) = \frac{5}{4} \times \left( \frac{4}{21} - \frac{3}{21} \right) = \frac{5}{4} \times \frac{1}{21} = \frac{5}{84} \]

е)

• \[ 14.2 \times \frac{5}{9} - 12.4 \times \frac{5}{9} = \frac{5}{9} \times (14.2 - 12.4) = \frac{5}{9} \times 1.8 = \frac{5}{9} \times \frac{18}{10} = \frac{5}{9} \times \frac{9}{5} = 1 \]

Ответ: г) 9/7; д) 5/84; е) 1