Giải câu 3 trang 105 toán VNEN 4 tập 2

a.

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

$\frac{8}{21}:\frac{2}{4}=\frac{8}{21}\times \frac{4}{2}=\frac{32}{42}$

$\frac{3}{11}\times 2=\frac{2\times 2}{11}=\frac{6}{11}$

b.

$4\times \frac{2}{7}=\frac{4\times 2}{7}=\frac{8}{7}$

$\frac{8}{5}:\frac{2}{5}=\frac{8}{5}\times \frac{5}{2}=\frac{40}{10}= 4$

$\frac{6}{13}: 2=\frac{6}{13}\times \frac{1}{2}=\frac{6}{26}$