Bài 16 trang 13 sgk Toán 7 tập 1, Tính: (-2/3 + 3/7) 4/5 + (-1/3 + 4/7) 4/5....

Bài 16. Tính

a) $(\frac{-2}{3} + \frac{3}{7}): \frac{4}{5} + (\frac{-1}{3} + \frac{4}{7}) : \frac{4}{5}$

b) $\frac{5}{9}: (\frac{1}{11} - \frac{5}{22}) + \frac{5}{9} :(\frac{1}{15} - \frac{2}{3})$

a)  $(\frac{-2}{3} + \frac{3}{7}): \frac{4}{5} + (\frac{-1}{3} + \frac{4}{7}) : \frac{4}{5}$

 = $(\frac{-2}{3}+ \frac{3}{7}+ \frac{-1}{3} +\frac{4}{7}):\frac{4}{5} = (\frac{-3}{3} +\frac{7}{7}): \frac{4}{5} = (-1+1):\frac{4}{5} = 0$

b) $\frac{5}{9}: (\frac{1}{11} - \frac{5}{22}) + \frac{5}{9} :(\frac{1}{15} - \frac{2}{3})$ = $\frac{5}{9}: \frac{2 - 5}{22} + \frac{5}{9}: \frac{1-10}{15} = \frac{5}{9}.\frac{22}{-3}+\frac{5}{9}.\frac{15}{-9} = \frac{5}{9}(\frac{22}{-3} + \frac{15}{-9})=\frac{5}{9}.\frac{-27}{3}= 5.(-1)=-5$