19. Вычислите: а) 6 1/3 − 8; б) −2 2/7 + 4 3/5; в) 5 1/3 − 6 1/4; г) 3/8 · (−9/16); д) 5/12 · (−6); е) −3 2/9 · 2/3; ж) 4/7 · (−49); з) −16 : (−4/9); и) −3 1/2 · (−1 3/7).

1. \(6\frac{1}{3}-8=\frac{19}{3}-\frac{24}{3}=-\frac{5}{3}=-1\frac{2}{3}\).
2. \(-2\frac{2}{7}+4\frac{3}{5}=-\frac{16}{7}+\frac{23}{5}=\frac{81}{35}=2\frac{11}{35}\).
3. \(5\frac{1}{3}-6\frac{1}{4}=\frac{16}{3}-\frac{25}{4}=-\frac{11}{12}\).
4. \(\frac{3}{8}\cdot\left(-\frac{9}{16}\right)=-\frac{27}{128}\).
5. \(\frac{5}{12}\cdot(-6)=-\frac{5}{2}=-2\frac{1}{2}\).
6. \(-3\frac{2}{9}\cdot\frac{2}{3}=-\frac{29}{9}\cdot\frac{2}{3}=-\frac{58}{27}=-2\frac{4}{27}\).
7. \(\frac{4}{7}\cdot(-49)=-28\).
8. \(-16:\left(-\frac{4}{9}\right)=(-16)\cdot\left(-\frac{9}{4}\right)=36\).
9. \(-3\frac{1}{2}\cdot\left(-1\frac{3}{7}\right)=-\frac{7}{2}\cdot\left(-\frac{10}{7}\right)=5\).

Ответ: а) −1 2/3; б) 2 11/35; в) −11/12; г) −27/128; д) −2 1/2; е) −2 4/27; ж) −28; з) 36; и) 5.