Tính a) 3/15 - 7/-8 + -1/3 b) 1/3 + 1/-5 -1/-6 + -1/8

* Hướng dẫn giải

a) $\frac{3}{15}-\frac{7}{-8}+\frac{-1}{3}=\frac{1}{5}+\frac{7}{8}-\frac{{\displaystyle 1}}{{\displaystyle 3}}$$=\frac{{\displaystyle 24}}{{\displaystyle 120}}+\frac{{\displaystyle 105}}{{\displaystyle 120}}-\frac{{\displaystyle 40}}{{\displaystyle 120}}=\frac{{\displaystyle 89}}{{\displaystyle 120}}$

b) $\frac{1}{3}+\frac{1}{-5}-\frac{1}{-6}+\frac{-1}{8}=\frac{1}{3}-\frac{1}{5}+\frac{1}{6}-\frac{1}{8}$$=\frac{40}{120}-\frac{24}{120}+\frac{20}{120}-\frac{15}{120}=\frac{21}{120}=\frac{7}{40}$