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{1}{3}$$=\frac{24}{120}+\frac{105}{120}-\frac{40}{120}=\frac{89}{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}$