6.58 Найдите сумму: a) \frac{8}{13} + \frac{3}{13}; б) \frac{31}{60} + \frac{29}{60}; в) 18 + \frac{4}{19}; г) 23 + \frac{9}{10}; д) 2\frac{7}{9} + \frac{8}{9}; ж) 4\frac{1}{2} + 3\frac{1}{4}; е) 15\frac{8}{11} + 4\frac{3}{11}; з) 5\frac{1}{7} + 3\frac{20}{21}.

a) \frac{8}{13} + \frac{3}{13} = \frac{8 + 3}{13} = \frac{11}{13} б) \frac{31}{60} + \frac{29}{60} = \frac{31 + 29}{60} = \frac{60}{60} = 1 в) 18 + \frac{4}{19} = 18\frac{4}{19} г) 23 + \frac{9}{10} = 23\frac{9}{10} д) 2\frac{7}{9} + \frac{8}{9} = 2 + \frac{7}{9} + \frac{8}{9} = 2 + \frac{7 + 8}{9} = 2 + \frac{15}{9} = 2 + 1\frac{6}{9} = 3\frac{6}{9} = 3\frac{2}{3} ж) 4\frac{1}{2} + 3\frac{1}{4} = 4 + \frac{1}{2} + 3 + \frac{1}{4} = 7 + \frac{1}{2} + \frac{1}{4} = 7 + \frac{2}{4} + \frac{1}{4} = 7 + \frac{3}{4} = 7\frac{3}{4} е) 15\frac{8}{11} + 4\frac{3}{11} = 15 + \frac{8}{11} + 4 + \frac{3}{11} = 19 + \frac{8}{11} + \frac{3}{11} = 19 + \frac{11}{11} = 19 + 1 = 20 з) 5\frac{1}{7} + 3\frac{20}{21} = 5 + \frac{1}{7} + 3 + \frac{20}{21} = 8 + \frac{3}{21} + \frac{20}{21} = 8 + \frac{23}{21} = 8 + 1\frac{2}{21} = 9\frac{2}{21}