71. Вычислите устно: a) 1- 4 7 . 2 : 3 7 - 1 1 3 ? б) 2- 5 9 : 13 . 9 - 23 ? B) 16 17 : 8 . 17 - 1 7 8 : 2 ? г) 1.2 43 + 1 3 : 4 . 4 5 ? д) 2 5 + 4 15 - 1 3 : 5 6 . 5 ?

a) 1 - $$\frac{4}{7}$$ = $$\frac{7}{7} - \frac{4}{7} = \frac{3}{7}$$; $$\frac{3}{7} \cdot 2 = \frac{6}{7}$$; $$\frac{6}{7} : \frac{3}{7} = \frac{6}{7} \cdot \frac{7}{3} = \frac{6}{3} = 2$$; $$2 - 1\frac{1}{3} = 2 - \frac{4}{3} = \frac{6}{3} - \frac{4}{3} = \frac{2}{3}$$. Ответ: $$\frac{2}{3}$$ б) 2 - $$\frac{5}{9} = \frac{18}{9} - \frac{5}{9} = \frac{13}{9}$$; $$\frac{13}{9} : 13 = \frac{13}{9} \cdot \frac{1}{13} = \frac{1}{9}$$; $$\frac{1}{9} \cdot 9 = 1$$; $$1 - 23 = -22$$. Ответ: -22 в) $$\frac{16}{17} : 8 = \frac{16}{17} \cdot \frac{1}{8} = \frac{2}{17}$$; $$\frac{2}{17} \cdot 17 = 2$$; $$2 - 1\frac{7}{8} = 2 - \frac{15}{8} = \frac{16}{8} - \frac{15}{8} = \frac{1}{8}$$; $$\frac{1}{8} : 2 = \frac{1}{8} \cdot \frac{1}{2} = \frac{1}{16}$$. Ответ: $$\frac{1}{16}$$ г) $$1\frac{1}{4} \cdot \frac{2}{3} = \frac{5}{4} \cdot \frac{2}{3} = \frac{10}{12} = \frac{5}{6}$$; $$\frac{5}{6} + \frac{1}{3} = \frac{5}{6} + \frac{2}{6} = \frac{7}{6}$$; $$\frac{7}{6} : 4 = \frac{7}{6} \cdot \frac{1}{4} = \frac{7}{24}$$; $$\frac{7}{24} \cdot \frac{4}{5} = \frac{28}{120} = \frac{7}{30}$$. Ответ: $$\frac{7}{30}$$ д) $$\frac{2}{5} + \frac{4}{15} = \frac{6}{15} + \frac{4}{15} = \frac{10}{15} = \frac{2}{3}$$; $$\frac{2}{3} - \frac{1}{3} = \frac{1}{3}$$; $$\frac{1}{3} : \frac{5}{6} = \frac{1}{3} \cdot \frac{6}{5} = \frac{6}{15} = \frac{2}{5}$$; $$\frac{2}{5} \cdot 5 = 2$$. Ответ: 2