一位飞镖运动员向一个目标投掷三次,记事件 Ai={A}_{i} =Ai= “第 iii 次命中目标” (i=1,2,3),P(A1)=18,P(Ai+1∣Ai)=2P(Ai)\left( {i = 1,2,3}\right) ,P\left( {A}_{1}\right) = \frac{1}{8},P\left( {{A}_{i + 1} \mid {A}_{i}}\right) = {2P}\left( {A}_{i}\right)(i=1,2,3),P(A1)=81,P(Ai+1∣Ai)=2P(Ai) , P(Ai+1∣Ai‾)=18(i=1,2)P\left( {{A}_{i + 1} \mid \overline{{A}_{i}}}\right) = \frac{1}{8}\left( {i = 1,2}\right)P(Ai+1∣Ai)=81(i=1,2) ,则 P(A3)=P\left( {A}_{3}\right) =P(A3)= ___.