59. Найдите значение выражения: а) (11/4 + 9/5) : 13/12; б) 1 : (1/3 + 1/12); в) 25/18 : (3/8 − 4/9); г) (1 1/15 + 4/7) · 21.

а) \(\left(\frac{11}{4}+\frac{9}{5}\right):\frac{13}{12}=\frac{91}{20}\cdot\frac{12}{13}=\frac{21}{5}\).

б) \(1:\left(\frac13+\frac1{12}\right)=1:\frac5{12}=\frac{12}{5}\).

в) \(\frac{25}{18}:\left(\frac38-\frac49\right)=\frac{25}{18}:\left(-\frac5{72}\right)=-20\).

г) \(\left(1\frac1{15}+\frac47\right)\cdot21=\left(\frac{16}{15}+\frac47\right)\cdot21=\frac{172}{105}\cdot21=\frac{172}{5}=34\frac25\).

Ответ: а) \(\frac{21}{5}\); б) \(\frac{12}{5}\); в) −20; г) \(34\frac25\).