Laske.

a) [[$\dfrac{1}{2}\cdot \dfrac{2}{3}-\dfrac{1}{4}$]] =

b) [[$\dfrac{1}{2}\cdot \left( \dfrac{2}{3}-\dfrac{1}{4} \right) $]] =

c) [[$ \dfrac{8}{9} - \dfrac{1}{2} : \dfrac{4}{5} $]] =

d) [[$ \left( \dfrac{8}{9} - \dfrac{1}{2} \right) : \dfrac{4}{5} $]] =