Giải câu 1 trang 24 sách toán VNEN lớp 6 tập 2

a) $\frac{-3}{-7} + \frac{5}{19} + \frac{-4}{7} = \frac{3 + (-4)}{7} + \frac{5}{19} = \frac{-1}{7} + \frac{5}{19} = \frac{(-1)\times 19 + 5\times 7}{133} = \frac{16}{133}$.

b) $\frac{-13}{24} + \frac{-5}{24} + \frac{7}{21} = \frac{-13}{24} + \frac{-5}{24} + \frac{1}{3} = \frac{-13}{24} + \frac{-5}{24} + \frac{8}{24} = \frac{-13 + (-5) + 8}{24} = \frac{-10}{24} = \frac{-5}{12}$.

c) $\frac{-5}{13} + (\frac{-8}{13} + 1) = (\frac{-5 + (-8)}{13} + 1 = (-1) + 1 = 0$;

d) $\frac{2}{3} + (\frac{3}{8} + \frac{-2}{3} = (\frac{2}{3} + \frac{-2}{3}) + \frac{3}{8} = 0 + \frac{3}{8} = \frac{3}{8}$;

e) $(\frac{-3}{4} + \frac{5}{8}) + \frac{-1}{8} = \frac{-3}{4} + \frac{5 + (-1)}{8} = \frac{-3}{4} + \frac{4}{8} = \frac{-3}{4} + \frac{2}{4} = \frac{-3 + 2}{4} = \frac{-1}{4}$.