Вычислите: 1) 1/4 + 1/12; 2) 1/6 + 2/3; 3) 7/8 + 3/4; 4) 4/7 + 2/21; 5) 9/12 + 3/4; 6) 8/9 + 1/3; 7) 4/5 + 7/15; 8) 2/21 + 5/14; 9) 3/18 + 5/27; 10) 3/15 + 7/20.

1. \(\frac{1}{4}+\frac{1}{12}=\frac{3}{12}+\frac{1}{12}=\frac{1}{3}\).
2. \(\frac{1}{6}+\frac{2}{3}=\frac{1}{6}+\frac{4}{6}=\frac{5}{6}\).
3. \(\frac{7}{8}+\frac{3}{4}=\frac{7}{8}+\frac{6}{8}=\frac{13}{8}\).
4. \(\frac{4}{7}+\frac{2}{21}=\frac{12}{21}+\frac{2}{21}=\frac{14}{21}=\frac{2}{3}\).
5. \(\frac{9}{12}+\frac{3}{4}=\frac{3}{4}+\frac{3}{4}=\frac{3}{2}\).
6. \(\frac{8}{9}+\frac{1}{3}=\frac{8}{9}+\frac{3}{9}=\frac{11}{9}\).
7. \(\frac{4}{5}+\frac{7}{15}=\frac{12}{15}+\frac{7}{15}=\frac{19}{15}\).
8. \(\frac{2}{21}+\frac{5}{14}=\frac{4}{42}+\frac{15}{42}=\frac{19}{42}\).
9. \(\frac{3}{18}+\frac{5}{27}=\frac{1}{6}+\frac{5}{27}=\frac{9}{54}+\frac{10}{54}=\frac{19}{54}\).
10. \(\frac{3}{15}+\frac{7}{20}=\frac{1}{5}+\frac{7}{20}=\frac{4}{20}+\frac{7}{20}=\frac{11}{20}\).

Ответ: 1) \(\frac{1}{3}\); 2) \(\frac{5}{6}\); 3) \(\frac{13}{8}\); 4) \(\frac{2}{3}\); 5) \(\frac{3}{2}\); 6) \(\frac{11}{9}\); 7) \(\frac{19}{15}\); 8) \(\frac{19}{42}\); 9) \(\frac{19}{54}\); 10) \(\frac{11}{20}\).