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1) $(\frac{7}{15} - \frac{1}{6}) + \frac{2}{5} = \frac{14}{30} - \frac{5}{30} = \frac{9}{30} + \frac{2}{5} = \frac{9}{30} + \frac{12}{30} = \frac{21}{30} = \frac{7}{10} = 0,7$

НОЗ: 30, 30.

2) $(\frac{3}{8} - \frac{1}{9}) + \frac{25}{36} = \frac{27}{72} - \frac{8}{72} = \frac{19}{72} + \frac{25}{36} = \frac{19}{72} + \frac{50}{72} = \frac{69}{72}$

НОЗ: 72.

3) $(\frac{8}{9} - \frac{5}{6}) + \frac{2}{3} = \frac{16}{18} - \frac{15}{18} = \frac{1}{18} + \frac{2}{3} = \frac{1}{18} + \frac{12}{18} = \frac{13}{18}$

НОЗ: 18.

4) $(\frac{7}{8} - \frac{13}{20} + \frac{9}{10} = \frac{35}{40} - \frac{26}{40} = \frac{9}{40} + \frac{9}{10} = \frac{9}{40} + \frac{36}{40} = \frac{45}{40} = 1\frac{5}{40}$

НОЗ: 40.

5) $(\frac{7}{18} - \frac{1}{12}) + \frac{5}{6} = \frac{14}{36} - \frac{3}{36} = \frac{11}{36} + \frac{30}{36} = \frac{41}{36} = 1\frac{5}{36}$

НОЗ: 36.

6) $(\frac{3}{4} - \frac{8}{15}) + \frac{17}{20} = \frac{x}{y} = \frac{45}{60} - \frac{32}{60} = \frac{13}{60} + \frac{51}{60} = \frac{64}{60} = 1\frac{4}{60}$

НОЗ: 60.