Выполните сложение или вычитание дробей

**Ответы:** 1) $$\frac{1}{3} + \frac{3}{8} = \frac{1 \cdot 8}{3 \cdot 8} + \frac{3 \cdot 3}{8 \cdot 3} = \frac{8}{24} + \frac{9}{24} = \frac{17}{24}$$ 2) $$\frac{2}{7} + \frac{5}{14} = \frac{2 \cdot 2}{7 \cdot 2} + \frac{5}{14} = \frac{4}{14} + \frac{5}{14} = \frac{9}{14}$$ 3) $$\frac{3}{5} + \frac{4}{15} = \frac{3 \cdot 3}{5 \cdot 3} + \frac{4}{15} = \frac{9}{15} + \frac{4}{15} = \frac{13}{15}$$ 4) $$\frac{1}{8} + \frac{3}{16} = \frac{1 \cdot 2}{8 \cdot 2} + \frac{3}{16} = \frac{2}{16} + \frac{3}{16} = \frac{5}{16}$$ 5) $$\frac{2}{9} + \frac{5}{18} = \frac{2 \cdot 2}{9 \cdot 2} + \frac{5}{18} = \frac{4}{18} + \frac{5}{18} = \frac{9}{18} = \frac{1}{2}$$ 6) $$\frac{8}{13} - \frac{1}{26} = \frac{8 \cdot 2}{13 \cdot 2} - \frac{1}{26} = \frac{16}{26} - \frac{1}{26} = \frac{15}{26}$$ 7) $$\frac{7}{15} - \frac{7}{30} = \frac{7 \cdot 2}{15 \cdot 2} - \frac{7}{30} = \frac{14}{30} - \frac{7}{30} = \frac{7}{30}$$ 8) $$\frac{2}{19} - \frac{1}{38} = \frac{2 \cdot 2}{19 \cdot 2} - \frac{1}{38} = \frac{4}{38} - \frac{1}{38} = \frac{3}{38}$$ 9) $$\frac{5}{7} - \frac{3}{14} = \frac{5 \cdot 2}{7 \cdot 2} - \frac{3}{14} = \frac{10}{14} - \frac{3}{14} = \frac{7}{14} = \frac{1}{2}$$ 10) $$\frac{4}{21} - \frac{1}{7} = \frac{4}{21} - \frac{1 \cdot 3}{7 \cdot 3} = \frac{4}{21} - \frac{3}{21} = \frac{1}{21}$$ 11) $$\frac{7}{20} + \frac{11}{50} = \frac{7 \cdot 5}{20 \cdot 5} + \frac{11 \cdot 2}{50 \cdot 2} = \frac{35}{100} + \frac{22}{100} = \frac{57}{100} = 0,57$$