Tính một cách hợp lí. a) A = -3/14 + 2/13 + -25/14 + -15/13

* Hướng dẫn giải

a) A = $\frac{-3}{14}+\frac{2}{13}+\frac{-25}{14}+\frac{-15}{13}$

       = $\left(\frac{-3}{14}+\frac{-25}{14}\right)+\left(\frac{2}{13}+\frac{-15}{13}\right)$

       = $\left(\frac{-28}{14}\right)+\left(\frac{-13}{13}\right)$

       = (-2) + (-1) = -3

b) B = $\frac{5}{3}.\frac{7}{25}+\frac{5}{3}.\frac{21}{25}-\frac{5}{3}.\frac{7}{25}$

        = $\frac{5}{3}.\left(\frac{7}{25}+\frac{21}{25}-\frac{7}{25}\right)$

        = $\frac{5}{3}.\frac{21}{25}$ = $\frac{7}{5}$