Tính a. 2 / 5 + 3 / 4 b. 2 / 5 + 3 / 10 - 1 / 2 c. 8 / 11

* Hướng dẫn giải

$a.\frac{2}{5} + \frac{3}{4}=\frac{8}{20}+\frac{15}{20}=\frac{23}{20}$

$$\begin{gathered} \mathrm{b}. \frac{2}{5}+\frac{3}{10}-\frac{1}{2} \\ =\frac{4}{10}+\frac{3}{10}-\frac{1}{2} \\ =\frac{7}{10}-\frac{1}{2} \\ =\frac{7}{10}-\frac{5}{10} \\ =\frac{2}{10}=\frac{1}{5} \end{gathered}$$

$$\begin{gathered} c.\frac{8}{11}+\frac{8}{33}\times \frac{3}{4} \\ =\frac{8}{11}+\frac{24}{132} \\ =\frac{8}{11}-\frac{2}{11} \\ =\frac{6}{11} \end{gathered}$$