A Table of Joint Probabilities Is Shown Below Calculate P $A _ { 1 }$

Essay

A table of joint probabilities is shown below. $$\begin{array} { | c | c | c | c | } \hline & A _ { 1 } & A _ { 2 } & A _ { 3 } \\\hline B _ { 1 } & 0.15 & 0.25 & 0.20 \\\hline B _ { 2 } & 0.10 & 0.15 & 0.15 \\\hline\end{array}$$ Calculate P( $A _ { 1 }$  $B _ { 1 }$ ).