Tính: a) 3/4 + -6/7 + 9/ -14 b) 1/3 - -1/4 - 5/12

* Hướng dẫn giải

a) $\frac{3}{4}+\frac{-6}{7}+\frac{9}{-14}=\frac{3}{4}+\frac{-6}{7}+\frac{-9}{14}$$=\frac{21}{28}+\frac{-24}{28}+\frac{-18}{28}=\frac{-21}{28}=\frac{-3}{4}$

b) $\frac{1}{3}-\frac{-1}{4}-\frac{5}{12}=\frac{1}{12}+\frac{3}{12}-\frac{5}{12}=\frac{-1}{12}$