Đ, S?

a) \(\dfrac{11}{12}-\dfrac{1}{4}=\dfrac{8}{12}=\dfrac{2}{3}\)                           b) \(\dfrac{5}{9}+\dfrac{4}{3}=\dfrac{9}{12}=\dfrac{3}{4}\) 

c) \(\dfrac{3}{10}\times\dfrac{5}{6}=\dfrac{15}{60}=\dfrac{1}{4}\)                           d) \(\dfrac{15}{8}:\dfrac{3}{4}=\dfrac{60}{24}=\dfrac{5}{2}\)