Tính a) -6/18 + 18/27

a) $\frac{-6}{18}+\frac{18}{27}=\frac{-1}{3}+\frac{2}{3}=\frac{1}{3}.$

b) $\mathrm{2,5}-\left(-\frac{6}{9}\right)=\frac{5}{2}+\frac{2}{3}=\frac{15}{6}+\frac{4}{6}=\frac{19}{6}.$

c) –0,32.(–0,875) $-\mathrm{0,32.}\left(-\mathrm{0,875}\right)=\frac{-32}{100}.\frac{-875}{1000}=\frac{-8}{25}.\frac{-7}{8}=\frac{\left(-8\right).\left(-7\right)}{25.8}=\frac{7}{25}.$

d) $\left(-5\right):2\frac{1}{5}=-5:\frac{11}{5}=-5.\frac{5}{11}=\frac{-25}{11}.$