Ответ:

[tex]1) \frac{1}{4} + \frac{1}{5}\\ \\ \frac{5+4}{20} \\\\\frac{9}{20}[/tex]

[tex]2) \frac{1}{2} + \frac{7}{9} \\\\\frac{9+14}{18} \\\\\frac{23}{18} \\\\3) \frac{2}{3} - \frac{2}{5}\\ \\\frac{10-6}{15} \\\\\frac{4}{15} \\\\4) \frac{5}{7} - \frac{1}{6} \\\\\frac{30-7}{42} \\\\\frac{23}{42} \\\\5) \frac{5}{7} - \frac{3}{14} \\\\\frac{10-3}{14} \\\\\frac{7}{14} \\\\\frac{1}{2} \\\\6)\frac{5}{6} - \frac{3}{8} \\\\\frac{20-9}{24} \\\\\frac{11}{24} \\\\7) \frac{7}{12} - \frac{5}{36} \\\\\frac{21-5}{36} \\\\\frac{16}{36} \\\\\frac{4}{9} \\\\[/tex]

[tex]8) \frac{2}{15} + \frac{1}{6} \\\\\frac{4+5}{30} \\\\\frac{9}{30} \\\\\frac{3}{10} \\\\9) \frac{5}{12} - \frac{2}{9} \\\\\frac{15-8}{36} \\\\\frac{7}{36} \\\\10) \frac{9}{20} - \frac{11}{30} \\\\\frac{27-22}{60} \\\\\frac{5}{60} \\\\\frac{1}{12} \\\\11) \frac{21}{22} - \frac{3}{55} \\\\\frac{105-6}{110} \\\\\frac{99}{110} \\\\\frac{9}{10} \\\\12) \frac{5}{9} + \frac{1}{2} + \frac{7}{12} \\\\\frac{20+18+21}{36} \\\\\frac{59}{36} \\\\1\frac{23}{36}[/tex]

Я долго делал 20 минут