5.445 Вычислите: а) 1/2 + 1/3; б) 1/3 + 2/7; в) 2/5 + 1/3; г) 3/7 + 4/9; д) 5/9 - 1/6; е) 3/4 - 1/3; ж) 1/6 + 1/3; з) 9/5 - 7/10; и) 1/2 - 3/8; к) 7/15 - 3/10; л) 3/8 + 5/12; м) 5/9 - 1/6; н) 5/11 + 3/5; о) 17/30 - 3/6; п) 17/35 - 4/15.

**Ответы:** а) $\frac{1}{2} + \frac{1}{3} = \frac{3}{6} + \frac{2}{6} = \frac{5}{6}$ б) $\frac{1}{3} + \frac{2}{7} = \frac{7}{21} + \frac{6}{21} = \frac{13}{21}$ в) $\frac{2}{5} + \frac{1}{3} = \frac{6}{15} + \frac{5}{15} = \frac{11}{15}$ г) $\frac{3}{7} + \frac{4}{9} = \frac{27}{63} + \frac{28}{63} = \frac{55}{63}$ д) $\frac{5}{9} - \frac{1}{6} = \frac{10}{18} - \frac{3}{18} = \frac{7}{18}$ е) $\frac{3}{4} - \frac{1}{3} = \frac{9}{12} - \frac{4}{12} = \frac{5}{12}$ ж) $\frac{1}{6} + \frac{1}{3} = \frac{1}{6} + \frac{2}{6} = \frac{3}{6} = \frac{1}{2}$ з) $\frac{9}{5} - \frac{7}{10} = \frac{18}{10} - \frac{7}{10} = \frac{11}{10} = 1\frac{1}{10}$ и) $\frac{1}{2} - \frac{3}{8} = \frac{4}{8} - \frac{3}{8} = \frac{1}{8}$ к) $\frac{7}{15} - \frac{3}{10} = \frac{14}{30} - \frac{9}{30} = \frac{5}{30} = \frac{1}{6}$ л) $\frac{3}{8} + \frac{5}{12} = \frac{9}{24} + \frac{10}{24} = \frac{19}{24}$ м) $\frac{5}{9} - \frac{1}{6} = \frac{10}{18} - \frac{3}{18} = \frac{7}{18}$ н) $\frac{5}{11} + \frac{3}{5} = \frac{25}{55} + \frac{33}{55} = \frac{58}{55} = 1\frac{3}{55}$ о) $\frac{17}{30} - \frac{3}{6} = \frac{17}{30} - \frac{15}{30} = \frac{2}{30} = \frac{1}{15}$ п) $\frac{17}{35} - \frac{4}{15} = \frac{51}{105} - \frac{28}{105} = \frac{23}{105}$