Вариант 2: 1) \(\frac{1}{4} + \frac{1}{12}\) 2) \(\frac{1}{6} + \frac{2}{3}\) 3) \(\frac{7}{8} + \frac{3}{4}\) 4) \(\frac{4}{7} + \frac{2}{21}\) 5) \(\frac{9}{12} + \frac{3}{4}\) 6) \(\frac{8}{9} + \frac{1}{3}\) 7) \(\frac{4}{5} + \frac{7}{15}\) 8) \(\frac{2}{21} + \frac{5}{14}\) 9) \(\frac{3}{18} + \frac{5}{27}\) 10) \(\frac{3}{15} + \frac{7}{20}\)

Вариант 2

1. \(\frac{1}{4} + \frac{1}{12} = \frac{1 \times 3}{4 \times 3} + \frac{1}{12} = \frac{3}{12} + \frac{1}{12} = \frac{3+1}{12} = \frac{4}{12} = \frac{1}{3}\)

2. \(\frac{1}{6} + \frac{2}{3} = \frac{1}{6} + \frac{2 \times 2}{3 \times 2} = \frac{1}{6} + \frac{4}{6} = \frac{1+4}{6} = \frac{5}{6}\)

3. \(\frac{7}{8} + \frac{3}{4} = \frac{7}{8} + \frac{3 \times 2}{4 \times 2} = \frac{7}{8} + \frac{6}{8} = \frac{7+6}{8} = \frac{13}{8} = 1\frac{5}{8}\)

4. \(\frac{4}{7} + \frac{2}{21} = \frac{4 \times 3}{7 \times 3} + \frac{2}{21} = \frac{12}{21} + \frac{2}{21} = \frac{12+2}{21} = \frac{14}{21} = \frac{2}{3}\)

5. \(\frac{9}{12} + \frac{3}{4} = \frac{3}{4} + \frac{3}{4} = \frac{3+3}{4} = \frac{6}{4} = \frac{3}{2} = 1\frac{1}{2}\)

6. \(\frac{8}{9} + \frac{1}{3} = \frac{8}{9} + \frac{1 \times 3}{3 \times 3} = \frac{8}{9} + \frac{3}{9} = \frac{8+3}{9} = \frac{11}{9} = 1\frac{2}{9}\)

7. \(\frac{4}{5} + \frac{7}{15} = \frac{4 \times 3}{5 \times 3} + \frac{7}{15} = \frac{12}{15} + \frac{7}{15} = \frac{12+7}{15} = \frac{19}{15} = 1\frac{4}{15}\)

8. \(\frac{2}{21} + \frac{5}{14} = \frac{2 \times 2}{21 \times 2} + \frac{5 \times 3}{14 \times 3} = \frac{4}{42} + \frac{15}{42} = \frac{4+15}{42} = \frac{19}{42}\)

9. \(\frac{3}{18} + \frac{5}{27} = \frac{1}{6} + \frac{5}{27} = \frac{1 \times 9}{6 \times 9} + \frac{5 \times 2}{27 \times 2} = \frac{9}{54} + \frac{10}{54} = \frac{9+10}{54} = \frac{19}{54}\)

10. \(\frac{3}{15} + \frac{7}{20} = \frac{1}{5} + \frac{7}{20} = \frac{1 \times 4}{5 \times 4} + \frac{7}{20} = \frac{4}{20} + \frac{7}{20} = \frac{4+7}{20} = \frac{11}{20}\)