Задание 7. Решите: а) 5/4 + (−7 3/4 + 7/4 · 2 2/7) : 5/9; б) 24/39 · (1/2 + 7/12) − 8/9 : 10/21

а)

\(2\frac{2}{7}=\frac{16}{7}\), поэтому \(\frac{7}{4}\cdot\frac{16}{7}=4\).

\(-7\frac{3}{4}+4=-\frac{31}{4}+\frac{16}{4}=-\frac{15}{4}\).

\(\frac{5}{4}+\left(-\frac{15}{4}\right):\frac{5}{9}=\frac{5}{4}-\frac{15}{4}\cdot\frac{9}{5}=\frac{5}{4}-\frac{27}{4}=-\frac{22}{4}=-\frac{11}{2}\).

б)

\(\frac{24}{39}=\frac{8}{13}\), а \(\frac{1}{2}+\frac{7}{12}=\frac{6}{12}+\frac{7}{12}=\frac{13}{12}\).

\(\frac{8}{13}\cdot\frac{13}{12}=\frac{2}{3}\).

\(\frac{8}{9}:\frac{10}{21}=\frac{8}{9}\cdot\frac{21}{10}=\frac{28}{15}\).

\(\frac{2}{3}-\frac{28}{15}=\frac{10}{15}-\frac{28}{15}=-\frac{18}{15}=-\frac{6}{5}\).

Ответ: а) \(-\frac{11}{2}\); б) \(-\frac{6}{5}\).