Let r = rain and p = practice.
Therefore,
[tex]\begin{gathered} Pr\mleft(p\mright)=Pr\mleft(r\mright)\times Pr\mleft(p|r\mright)+1-Pr\mleft(r\mright)\times Pr\mleft(p|notr\mright) \\ Pr(p)=0.5\times0.6\text{ +0.5 x 0.4} \\ =0.3\text{ +0.2} \\ =0.5 \end{gathered}[/tex]