If $\mathrm{A}$ and $\mathrm{B}$ are such that $P\left(\mathrm{~A}^{\prime} \cup \mathrm{B}^{\prime}\right)=\frac{2}{3}$ and $\mathrm{P}(\mathrm{A} \cup \mathrm{B})=\frac{5}{9}$, then $\mathrm{P}\left(\mathrm{A}^{\prime}\right)+\mathrm{P}\left(\mathrm{B}^{\prime}\right)=$