19. Вычислите: 1) 3/5 + (−2/3); 2) −3/7 + 3/5; 3) 5/12 + (−3/10); 4) −7/8 + 1 5/6; 5) −1 1/6 + 1 5/18; 6) 2 4/15 + (−5/6); 7) −5 7/12 + 3 5/8.

1. \(\frac35-\frac23=\frac9{15}-\frac{10}{15}=-\frac1{15}\).
2. \(-\frac37+\frac35=-\frac{15}{35}+\frac{21}{35}=\frac6{35}\).
3. \(\frac5{12}-\frac3{10}=\frac{25}{60}-\frac{18}{60}=\frac7{60}\).
4. \(-\frac78+1\frac56=-\frac78+\frac{11}{6}=-\frac{21}{24}+\frac{44}{24}=\frac{23}{24}\).
5. \(-1\frac16+1\frac5{18}=-\frac76+\frac{23}{18}=-\frac{21}{18}+\frac{23}{18}=\frac19\).
6. \(2\frac4{15}-\frac56=\frac{34}{15}-\frac56=\frac{68}{30}-\frac{25}{30}=\frac{43}{30}=1\frac{13}{30}\).
7. \(-5\frac7{12}+3\frac58=-\frac{67}{12}+\frac{29}{8}=-\frac{134}{24}+\frac{87}{24}=-\frac{47}{24}=-1\frac{23}{24}\).

Ответ: 1) \(-\frac1{15}\); 2) \(\frac6{35}\); 3) \(\frac7{60}\); 4) \(\frac{23}{24}\); 5) \(\frac19\); 6) \(1\frac{13}{30}\); 7) \(-1\frac{23}{24}\).