269. Вычислите: 1) $$\frac{1}{4} + \frac{3}{5}$$; 2) $$\frac{9}{11} - \frac{2}{5}$$; 3) $$\frac{13}{16} - \frac{9}{32}$$; 4) $$\frac{3}{28} + \frac{5}{14}$$; 5) $$\frac{14}{15} - \frac{7}{10}$$; 6) $$\frac{3}{8} + \frac{1}{6}$$; 7) $$\frac{9}{25} - \frac{7}{20}$$; 8) $$\frac{37}{42} - \frac{17}{24}$$; 9) $$\frac{11}{24} - \frac{3}{16}$$; 10) $$\frac{9}{16} + \frac{7}{24} - \frac{3}{8}$$; 11) $$\frac{1}{3} - \frac{1}{6} + \frac{1}{4}$$; 12) $$\frac{2}{5} + \frac{4}{15} - \frac{5}{9}$$

Решение заданий 269: 1) $$\frac{1}{4} + \frac{3}{5} = \frac{1*5}{4*5} + \frac{3*4}{5*4} = \frac{5}{20} + \frac{12}{20} = \frac{17}{20}$$ 2) $$\frac{9}{11} - \frac{2}{5} = \frac{9*5}{11*5} - \frac{2*11}{5*11} = \frac{45}{55} - \frac{22}{55} = \frac{23}{55}$$ 3) $$\frac{13}{16} - \frac{9}{32} = \frac{13*2}{16*2} - \frac{9}{32} = \frac{26}{32} - \frac{9}{32} = \frac{17}{32}$$ 4) $$\frac{3}{28} + \frac{5}{14} = \frac{3}{28} + \frac{5*2}{14*2} = \frac{3}{28} + \frac{10}{28} = \frac{13}{28}$$ 5) $$\frac{14}{15} - \frac{7}{10} = \frac{14*2}{15*2} - \frac{7*3}{10*3} = \frac{28}{30} - \frac{21}{30} = \frac{7}{30}$$ 6) $$\frac{3}{8} + \frac{1}{6} = \frac{3*3}{8*3} + \frac{1*4}{6*4} = \frac{9}{24} + \frac{4}{24} = \frac{13}{24}$$ 7) $$\frac{9}{25} - \frac{7}{20} = \frac{9*4}{25*4} - \frac{7*5}{20*5} = \frac{36}{100} - \frac{35}{100} = \frac{1}{100}$$ 8) $$\frac{37}{42} - \frac{17}{24} = \frac{37*4}{42*4} - \frac{17*7}{24*7} = \frac{148}{168} - \frac{119}{168} = \frac{29}{168}$$ 9) $$\frac{11}{24} - \frac{3}{16} = \frac{11*2}{24*2} - \frac{3*3}{16*3} = \frac{22}{48} - \frac{9}{48} = \frac{13}{48}$$ 10) $$\frac{9}{16} + \frac{7}{24} - \frac{3}{8} = \frac{9*3}{16*3} + \frac{7*2}{24*2} - \frac{3*6}{8*6} = \frac{27}{48} + \frac{14}{48} - \frac{18}{48} = \frac{41}{48} - \frac{18}{48} = \frac{23}{48}$$ 11) $$\frac{1}{3} - \frac{1}{6} + \frac{1}{4} = \frac{1*4}{3*4} - \frac{1*2}{6*2} + \frac{1*3}{4*3} = \frac{4}{12} - \frac{2}{12} + \frac{3}{12} = \frac{2}{12} + \frac{3}{12} = \frac{5}{12}$$ 12) $$\frac{2}{5} + \frac{4}{15} - \frac{5}{9} = \frac{2*9}{5*9} + \frac{4*3}{15*3} - \frac{5*5}{9*5} = \frac{18}{45} + \frac{12}{45} - \frac{25}{45} = \frac{30}{45} - \frac{25}{45} = \frac{5}{45} = \frac{1}{9}