Calculate.

a) [[$ \displaystyle\frac {4} {5} \cdot 2 = $]]

b) [[$ \displaystyle\frac {1} {3} \cdot \displaystyle\frac {4} {3} = $]]

c) [[$ \displaystyle\frac {2} {5} : \displaystyle\frac {1} {2} = $]]

d) [[$ \displaystyle\frac {3} {7} : 3 = $]]