Задание 4. Вычислить: а) 3/10 − 13/15; б) −6/7 + (−3/14); в) 5/9 + (−5/6); г) −6/20 + 7/15; д) −4/5 − 8/25; е) 7/12 − (−8/15); ж) −4/9 − (−12/27).

1. \(\frac{3}{10}-\frac{13}{15}=\frac{9}{30}-\frac{26}{30}=-\frac{17}{30}\).
2. \(-\frac{6}{7}+\left(-\frac{3}{14}\right)=-\frac{12}{14}-\frac{3}{14}=-\frac{15}{14}\).
3. \(\frac{5}{9}+\left(-\frac{5}{6}\right)=\frac{10}{18}-\frac{15}{18}=-\frac{5}{18}\).
4. \(-\frac{6}{20}+\frac{7}{15}=-\frac{3}{10}+\frac{7}{15}=-\frac{9}{30}+\frac{14}{30}=\frac{1}{6}\).
5. \(-\frac{4}{5}-\frac{8}{25}=-\frac{20}{25}-\frac{8}{25}=-\frac{28}{25}\).
6. \(\frac{7}{12}-\left(-\frac{8}{15}\right)=\frac{35}{60}+\frac{32}{60}=\frac{67}{60}\).
7. \(-\frac{4}{9}-\left(-\frac{12}{27}\right)=-\frac{4}{9}+\frac{4}{9}=0\).

Ответ: а) \(-\frac{17}{30}\); б) \(-\frac{15}{14}\); в) \(-\frac{5}{18}\); г) \(\frac{1}{6}\); д) \(-\frac{28}{25}\); е) \(\frac{67}{60}\); ж) 0.