Giải câu 2 trang 38 Cánh Diều Toán 6 tập 2.
a) $\frac{2}{9}$ + $\frac{-3}{10}$ + $\frac{-7}{10}$ = $\frac{2}{9}$ + ( $\frac{-3}{10}$ + $\frac{-7}{10}$ ) = $\frac{2}{9}$ + $\frac{-10}{10}$ = $\frac{2}{9}$ + (-1) = $\frac{2}{9}$ + $\frac{-9}{9}$ = $\frac{-7}{9}$
b) $\frac{-11}{6}$ + $\frac{2}{5}$ + $\frac{-1}{6}$ = ( $\frac{-11}{6}$ + $\frac{-1}{6}$ ) + $\frac{2}{5}$ = $\frac{-12}{6}$ + $\frac{2}{5}$ = - 2 + $\frac{2}{5}$ = $\frac{(-2) . 5}{5}$ + $\frac{2}{5}$ = $\frac{-10}{5}$ + $\frac{2}{5}$ = $\frac{-8}{5}$
c) $\frac{-5}{8}$ + $\frac{12}{7}$ + $\frac{13}{8}$ + $\frac{2}{7}$ = ( $\frac{-5}{8}$ + $\frac{13}{8}$ ) + ( $\frac{12}{7}$ + $\frac{2}{7}$ ) = $\frac{8}{8}$ + $\frac{14}{7}$ = 1 + 2 = 3