Giải bài 1 trang 136 - SGK Toán lớp 4

Tính rồi rút gọn:

a) $\dfrac{3}{5} : \dfrac{3}{4}=\dfrac{3}{5} \times\dfrac{4}{3}=\dfrac{12}{15}=\dfrac{4}{5}$       

$\dfrac{2}{5} : \dfrac{3}{10}=\dfrac{2}{5} \times\dfrac{10}{3}=\dfrac{20}{15}=\dfrac{4}{3}$           

$\dfrac{9}{8} : \dfrac{3}{4}=\dfrac{9}{8} \times\dfrac{4}{3}=\dfrac{36}{24}=\dfrac{3}{2}$                       

b) $\dfrac{1}{4} : \dfrac{1}{2}=\dfrac{1}{4} \times \dfrac{2}{1}=\dfrac{2}{4} = \dfrac{1}{2}$

$\dfrac{1}{8} : \dfrac{1}{6}=\dfrac{1}{8} \times\dfrac{6}{1}=\dfrac{6}{8} = \dfrac{3}{4}$         

$\dfrac{1}{5} : \dfrac{1}{10}=\dfrac{1}{5} \times\dfrac{10}{1}=\dfrac{10}{5} = 2$