4. Вычислите: 1) 5/9 + 4/7; 2) 8/9 − 13/18; 3) 11/12 − 9/16; 4) 3/8 + 7/10; 5) 9/14 − 12/35; 6) 16/21 − 2/9 + 5/7.

1. \(\frac{5}{9}+\frac{4}{7}=\frac{35}{63}+\frac{36}{63}=\frac{71}{63}=1\frac{8}{63}\).
2. \(\frac{8}{9}-\frac{13}{18}=\frac{16}{18}-\frac{13}{18}=\frac{3}{18}=\frac{1}{6}\).
3. \(\frac{11}{12}-\frac{9}{16}=\frac{44}{48}-\frac{27}{48}=\frac{17}{48}\).
4. \(\frac{3}{8}+\frac{7}{10}=\frac{15}{40}+\frac{28}{40}=\frac{43}{40}=1\frac{3}{40}\).
5. \(\frac{9}{14}-\frac{12}{35}=\frac{45}{70}-\frac{24}{70}=\frac{21}{70}=\frac{3}{10}\).
6. \(\frac{16}{21}-\frac{2}{9}+\frac{5}{7}=\frac{48}{63}-\frac{14}{63}+\frac{45}{63}=\frac{79}{63}=1\frac{16}{63}\).

Ответ: 1) 1 8/63; 2) 1/6; 3) 17/48; 4) 1 3/40; 5) 3/10; 6) 1 16/63.