Вариант 2. 4. Вычислите: 1) 3/7 + 2/9; 2) 2/3 − 1/6; 3) 13/20 − 7/15; 4) 11/16 + 5/12; 5) 9/14 − 8/21; 6) 19/30 − 2/5 + 1/3.

1. \(\frac{3}{7}+\frac{2}{9}=\frac{27}{63}+\frac{14}{63}=\frac{41}{63}\).

2. \(\frac{2}{3}-\frac{1}{6}=\frac{4}{6}-\frac{1}{6}=\frac{1}{2}\).

3. \(\frac{13}{20}-\frac{7}{15}=\frac{39}{60}-\frac{28}{60}=\frac{11}{60}\).

4. \(\frac{11}{16}+\frac{5}{12}=\frac{33}{48}+\frac{20}{48}=\frac{53}{48}=1\frac{5}{48}\).

5. \(\frac{9}{14}-\frac{8}{21}=\frac{27}{42}-\frac{16}{42}=\frac{11}{42}\).

6. \(\frac{19}{30}-\frac{2}{5}+\frac{1}{3}=\frac{19}{30}-\frac{12}{30}+\frac{10}{30}=\frac{17}{30}\).

Ответ: 1) 41/63; 2) 1/2; 3) 11/60; 4) 1 5/48; 5) 11/42; 6) 17/30.