№ 3. Выполните сложение, выбирая удобный порядок вычислений: 1) 7,29 + (-5,126) + (-6,29) + 5,126; 2) 0,74 + (-9,39) + 3,26 + (-10,61) + 5,25; 3) $$\frac{7}{16} + (-\frac{11}{42}) + (-\frac{9}{16}) + \frac{17}{42}$$; 4) $$-\frac{9}{40} + \frac{13}{50} + (-\frac{23}{50}) + \frac{19}{40}$$; 5) $$-3\frac{31}{36} + (-\frac{17}{24}) + 5\frac{4}{36} + (-\frac{2}{24})$$.

Решение: 1) 7,29 + (-5,126) + (-6,29) + 5,126 = 7,29 - 6,29 - 5,126 + 5,126 = (7,29 - 6,29) + (-5,126 + 5,126) = 1 + 0 = 1 Ответ: 1 2) 0,74 + (-9,39) + 3,26 + (-10,61) + 5,25 = 0,74 + 3,26 + 5,25 - 9,39 - 10,61 = (0,74 + 3,26) + 5,25 - (9,39 + 10,61) = 4 + 5,25 - 20 = 9,25 - 20 = -10,75 Ответ: -10,75 3) $$\frac{7}{16} + (-\frac{11}{42}) + (-\frac{9}{16}) + \frac{17}{42} = \frac{7}{16} - \frac{9}{16} - \frac{11}{42} + \frac{17}{42} = \frac{7 - 9}{16} + \frac{17 - 11}{42} = \frac{-2}{16} + \frac{6}{42} = -\frac{1}{8} + \frac{1}{7} = -\frac{7}{56} + \frac{8}{56} = \frac{1}{56}$$ Ответ: $$\frac{1}{56}$$ 4) $$-\frac{9}{40} + \frac{13}{50} + (-\frac{23}{50}) + \frac{19}{40} = -\frac{9}{40} + \frac{19}{40} + \frac{13}{50} - \frac{23}{50} = \frac{-9 + 19}{40} + \frac{13 - 23}{50} = \frac{10}{40} + \frac{-10}{50} = \frac{1}{4} - \frac{1}{5} = \frac{5}{20} - \frac{4}{20} = \frac{1}{20}$$ Ответ: $$\frac{1}{20}$$ 5) \begin{aligned} -3\frac{31}{36} + (-\frac{17}{24}) + 5\frac{4}{36} + (-\frac{2}{24}) &= -3\frac{31}{36} + 5\frac{4}{36} - \frac{17}{24} - \frac{2}{24} = 2\frac{-27}{36} - \frac{19}{24} = 1\frac{9}{36} - \frac{19}{24} = 1\frac{1}{4} - \frac{19}{24} = \frac{5}{4} - \frac{19}{24} = \frac{5 \cdot 6}{4 \cdot 6} - \frac{19}{24} = \frac{30}{24} - \frac{19}{24} = \frac{11}{24} \end{aligned} Ответ: $$\frac{11}{24}$$