969. Вычислите значение выражения: 1) −1/4 + 3/5; 2) 9/11 + (−2/5); 4) 7 5/12 + (−3 7/24); 5) −6 11/12 + (−8 13/18).

1. \(-\frac{1}{4}+\frac{3}{5}=-\frac{5}{20}+\frac{12}{20}=\frac{7}{20}\).
2. \(\frac{9}{11}+\left(-\frac{2}{5}\right)=\frac{9}{11}-\frac{2}{5}=\frac{45}{55}-\frac{22}{55}=\frac{23}{55}\).
3. \(7\frac{5}{12}+\left(-3\frac{7}{24}\right)=7\frac{10}{24}-3\frac{7}{24}=4\frac{3}{24}=4\frac{1}{8}\).
4. \(-6\frac{11}{12}+\left(-8\frac{13}{18}\right)=-\left(6\frac{11}{12}+8\frac{13}{18}\right)=-15\frac{23}{36}\).

Ответ: 1) 7/20; 2) 23/55; 4) 4 1/8; 5) −15 23/36.