Laske.

a) [[$ \dfrac{1}{2} + \dfrac{2}{3} $]] =

b) [[$ \dfrac{2}{3} - \dfrac{4}{5} $]] =

c) [[$ \dfrac{3}{4} + \dfrac{5}{6} $]] =

d) [[$ \dfrac{5}{6} - \dfrac{7}{8} $]] =