Tính nhanh: a) 1/3 + 3/8 + -4/3 b) -2/15 + 12/13 + -13/15 + -1/13

* Hướng dẫn giải

a) $\frac{1}{3}+\frac{3}{8}+\frac{-4}{3}=\left(\frac{1}{3}+\frac{-4}{3}\right)+\frac{3}{8}=-1+\frac{3}{8}=\frac{-5}{8}$

b) $\frac{-2}{15}+\frac{12}{13}+\frac{-13}{15}+\frac{-1}{13}=\left(\frac{-2}{15}+\frac{-13}{15}\right)+\left(\frac{12}{13}+\frac{-1}{13}\right)$$=-1+\frac{11}{13}=\frac{-2}{13}$