Tính a. 3 / 4 x ( 5 / 6 + 7 / 8) b. 3 / 10 + 7 / 3 : 5

* Hướng dẫn giải

$$\begin{gathered} \mathrm{a}. \frac{3}{4}\mathrm{x}\left(\frac{5}{6}+\frac{7}{8}\right) \\ = \frac{3}{4}\mathrm{x}\left(\frac{20}{24}+\frac{21}{24}\right) \\ =\frac{3}{4}\mathrm{x}\frac{41}{24} \\ =\frac{123}{96} \\ =\frac{41}{32} \\ \mathrm{b}. \frac{3}{10}+\frac{7}{3}:5 \\ =\frac{3}{10}+\frac{7}{3\mathrm{x}5} \\ =\frac{3}{10}+\frac{7}{15} \\ =\frac{9}{30}+\frac{14}{30} \\ =\frac{23}{30} \end{gathered}$$