№4. Выполните действия: а) (6rac{2}{25} + 7rac{23}{25} - 4rac{1}{40}) б) (20rac{1}{19} - 4rac{12}{19} - 5rac{17}{19}) в) ((6rac{5}{24} + 7rac{19}{24}) - (6rac{19}{23} - 5rac{9}{23}))

а) (6rac{2}{25} + 7rac{23}{25} - 4rac{1}{40} = (6+7-4) + (rac{2}{25} + rac{23}{25} - rac{1}{40}) = 9 + (rac{25}{25} - rac{1}{40}) = 9 + (1 - rac{1}{40}) = 9 + rac{39}{40} = 9rac{39}{40}) б) (20rac{1}{19} - 4rac{12}{19} - 5rac{17}{19} = (20-4-5) + (rac{1}{19} - rac{12}{19} - rac{17}{19}) = 11 - rac{28}{19} = 11 - 1rac{9}{19} = 10 - rac{9}{19} = 9rac{10}{19}) в) ((6rac{5}{24} + 7rac{19}{24}) - (6rac{19}{23} - 5rac{9}{23}) = (6+7) + (rac{5}{24} + rac{19}{24}) - ((6-5) + (rac{19}{23} - rac{9}{23})) = 13 + rac{24}{24} - (1 + rac{10}{23}) = 14 - 1 - rac{10}{23} = 13 - rac{10}{23} = 12rac{13}{23})