Задание №1. Вычислите: 1) 3/7 + 4/9; 2) 8/9 − 7/8; 3) 13/15 − 2/3; 4) 20/21 + 3/7; 5) 17/18 − 11/12; 6) 7/16 + 1/6.

1. \(\frac{3}{7}+\frac{4}{9}=\frac{27}{63}+\frac{28}{63}=\frac{55}{63}\).
2. \(\frac{8}{9}-\frac{7}{8}=\frac{64}{72}-\frac{63}{72}=\frac{1}{72}\).
3. \(\frac{13}{15}-\frac{2}{3}=\frac{13}{15}-\frac{10}{15}=\frac{1}{5}\).
4. \(\frac{20}{21}+\frac{3}{7}=\frac{20}{21}+\frac{9}{21}=\frac{29}{21}=1\frac{8}{21}\).
5. \(\frac{17}{18}-\frac{11}{12}=\frac{34}{36}-\frac{33}{36}=\frac{1}{36}\).
6. \(\frac{7}{16}+\frac{1}{6}=\frac{21}{48}+\frac{8}{48}=\frac{29}{48}\).

Ответ: 1) \(\frac{55}{63}\); 2) \(\frac{1}{72}\); 3) \(\frac{1}{5}\); 4) \(1\frac{8}{21}\); 5) \(\frac{1}{36}\); 6) \(\frac{29}{48}\).