No of black balls \(=5\) balls
No of red balls \(=3\) balls
Total balls \(=8\) balls
\(\operatorname{Pr}(\) a black ball and a red ball)
\(=\operatorname{Pr}\) ( 1 st ball red and \(2^{\text {nd }}\) ball black)
Or \(\operatorname{Pr}(1\) s ball black and 2 nd ball red)
\begin{aligned}
&=\left(\frac{3}{8} \times \frac{5}{7}\right)+\left(\frac{5}{8} \times \frac{3}{7}\right) \\
\frac{15}{56}+\frac{15}{56} &=\frac{30}{56}=\frac{15}{28}
\end{aligned}