Tính nhanh: a) -6/13 - (1 - -7/13) b) (1/9 + -5/17) + 3/6 + (-12/17 + -1/2) + 5/9

* Hướng dẫn giải

a) $\frac{-6}{13}-\left(1-\frac{-7}{13}\right)=\frac{-6}{13}-1+\frac{-7}{13}$$=\left(\frac{-6}{13}+\frac{-7}{13}\right)-1=-1-1=-2$

b) $\left(\frac{1}{9}+\frac{-5}{17}\right)+\frac{3}{6}+\left(\frac{-12}{17}+\frac{-1}{2}\right)+\frac{5}{9}$$=\frac{1}{9}+\frac{-5}{17}+\frac{3}{6}+\frac{-12}{17}+\frac{-1}{2}+\frac{5}{9}$$=\left(\frac{-5}{17}+\frac{-12}{17}\right)+\left(\frac{1}{9}+\frac{5}{9}\right)+\left(\frac{3}{6}+\frac{-1}{2}\right)$$=-1+\frac{2}{3}+0=\frac{-1}{3}$