Tính a. 4 / 5 + 1 / 3 b. 2 / 3 : 4 c. 13 / 7 - 7 / 7

* Hướng dẫn giải

$$\begin{gathered} \mathrm{a}. \frac{4}{5}+\frac{1}{3}=\frac{12}{15}+\frac{5}{15} \\ =\frac{12+5}{15}=\frac{17}{15} \end{gathered}$$

$$\begin{gathered} \mathrm{b}.\frac{2}{3}:4=\frac{2}{3} : \frac{4}{1} \\ = \frac{2 }{3 } \times \frac{1}{4}=\frac{2}{12}=\frac{1}{6} \end{gathered}$$

$\mathrm{c}. \frac{13}{7}-\frac{7}{7}=\frac{13-7}{7}=\frac{6}{7}$

$\mathrm{d}. \frac{4}{9}\mathrm{x}\frac{2}{5}=\frac{4 \times 2}{9\times 5}=\frac{8}{45}$