Giải bài 2 trang 137 - SGK Toán lớp 4

Mẫu: $\dfrac{3}{4} : 2 = \dfrac{3}{4} :\dfrac{2}{1}=\dfrac{3}{4} \times\dfrac{1}{2} =\dfrac{3}{8}$

Ta có thể rút gọn như sau:  $\dfrac{3}{4}: 2=\dfrac{3}{4\,\times\,2}=\dfrac{3}{8}$

a)$\dfrac{5}{7}: 3=\dfrac{5}{7\,\times\,3}=\dfrac{5}{35}=\dfrac{1}{7}$       

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

c) $\dfrac{2}{3}:4=\dfrac{2}{3\,\times\,4}=\dfrac{2}{12}=\dfrac{1}{6}$