Giải bài tập SGK Toán 4 Luyện tập trang 137 có đáp án

$\frac{2}{7}:\frac{4}{5}=\frac{2}{7}\times \frac{5}{4}=\frac{10}{28}=\frac{5}{14}$

$\frac{3}{8}:\frac{9}{4}=\frac{3}{8}\times \frac{4}{9}=\frac{12}{72}$

$\frac{8}{21}:\frac{4}{7}=\frac{8}{21}\times \frac{7}{4}=\frac{56}{84}=\frac{2}{3}$

$\frac{5}{8}:\frac{15}{8}=\frac{5}{8}\times \frac{8}{15}=\frac{40}{120}=\frac{1}{3}$

$$\begin{gathered} \left(\frac{1}{3}+\frac{1}{5}\right)\times \frac{1}{2}=\left(\frac{5}{15}+\frac{3}{15}\right)\times \frac{1}{2}=\frac{8}{15}\times \frac{1}{2}=\frac{8}{30} \\ \left(\frac{1}{3}+\frac{1}{5}\right)\times \frac{1}{2}=\frac{1}{3}\times \frac{1}{2}+\frac{1}{5}\times \frac{1}{2}=\frac{1}{6}+\frac{1}{10}=\frac{10}{60}+\frac{6}{60}=\frac{16}{60}=\frac{8}{30} \end{gathered}$$

$$\begin{gathered} \left(\frac{1}{3}-\frac{1}{5}\right)\times \frac{1}{2}=\left(\frac{5}{15}-\frac{3}{15}\right)\times \frac{1}{2}=\frac{2}{15}\times \frac{1}{2}=\frac{2}{30}=\frac{1}{15} \\ \left(\frac{1}{3}-\frac{1}{5}\right)\times \frac{1}{2}=\frac{1}{3}\times \frac{1}{2}-\frac{1}{5}\times \frac{1}{2}=\frac{1}{6}-\frac{1}{10}=\frac{10}{60}-\frac{6}{60}=\frac{4}{60}=\frac{1}{15} \end{gathered}$$