Вычислите. 4 вариант: 1) 1/4 + 2/7 =; 2) 5/7 − 1/3 =; 3) 2/3 · 6/7 =; 4) 3/5 : 1/4 =; 5) 2 3/4 + 1 5/7 =; 6) 1 1/4 − 1/3 =; 7) 1 1/2 · 2 2/9 =; 8) 4 1/6 : 2 1/3 =; 9) 2/3 + 1 =; 10) 1 − 1/5 =; 11) 2 · 1/5 =; 12) 7/9 : 3 =.

1. Приводим к общему знаменателю: \(\frac{1}{4}+\frac{2}{7}=\frac{7}{28}+\frac{8}{28}=\frac{15}{28}\).
2. \(\frac{5}{7}-\frac{1}{3}=\frac{15}{21}-\frac{7}{21}=\frac{8}{21}\).
3. \(\frac{2}{3}\cdot\frac{6}{7}=\frac{12}{21}=\frac{4}{7}\).
4. Деление заменяем умножением на обратную дробь: \(\frac{3}{5}:\frac{1}{4}=\frac{3}{5}\cdot4=\frac{12}{5}=2\frac{2}{5}\).
5. \(2\frac{3}{4}+1\frac{5}{7}=\frac{11}{4}+\frac{12}{7}=\frac{77+48}{28}=\frac{125}{28}=4\frac{13}{28}\).
6. \(1\frac{1}{4}-\frac{1}{3}=\frac{5}{4}-\frac{1}{3}=\frac{15-4}{12}=\frac{11}{12}\).
7. \(1\frac{1}{2}\cdot2\frac{2}{9}=\frac{3}{2}\cdot\frac{20}{9}=\frac{60}{18}=\frac{10}{3}=3\frac{1}{3}\).
8. \(4\frac{1}{6}:2\frac{1}{3}=\frac{25}{6}:\frac{7}{3}=\frac{25}{6}\cdot\frac{3}{7}=\frac{25}{14}=1\frac{11}{14}\).
9. \(\frac{2}{3}+1=\frac{2}{3}+\frac{3}{3}=\frac{5}{3}=1\frac{2}{3}\).
10. \(1-\frac{1}{5}=\frac{5}{5}-\frac{1}{5}=\frac{4}{5}\).
11. \(2\cdot\frac{1}{5}=\frac{2}{5}\).
12. \(\frac{7}{9}:3=\frac{7}{9}:\frac{3}{1}=\frac{7}{9}\cdot\frac{1}{3}=\frac{7}{27}\).

Ответ: 1) \(\frac{15}{28}\); 2) \(\frac{8}{21}\); 3) \(\frac{4}{7}\); 4) \(2\frac{2}{5}\); 5) \(4\frac{13}{28}\); 6) \(\frac{11}{12}\); 7) \(3\frac{1}{3}\); 8) \(1\frac{11}{14}\); 9) \(1\frac{2}{3}\); 10) \(\frac{4}{5}\); 11) \(\frac{2}{5}\); 12) \(\frac{7}{27}\).