Given that \({\rm{P}}\left( {\rm{A}} \right) = \dfrac{1}{5}{\rm{, P}}\left( {\rm{B}} \right) = \dfrac{1}{4}\) and \({\rm{P}}\left( {{\rm{A}} \cup {\rm{B}}} \right) = x\), and \(A\) and \(B\) are independent events then \(x =\,\,?{\rm{ }}\)