Example 3.15 : A privately owned business operates both a drive-in facility and a walk-in faclity. On a randomly selected day, let \( X \) and \( Y \), respectively, be the proportions of the time that the drive-in and the walk-in facilities are in use, and suppose that the joint density function of these random variables is
\[
f(x, y)=\left\{\begin{array}{ll}
\frac{2}{5}(2 x+3 y), & 0 \leq x \leq 1,0 \leq y \leq 1 \\
0, & \text { elsewhere }
\end{array}\right.
\]
(a) Verify condition 2 of Definition 3.9.
(b) Find \( P[(X, Y) \in \bar{A}] \), where \( \left.A=\widehat{\{(x, y)} \left\lvert\, 0<x<\frac{1}{2}\right., \frac{1}{4}<y<\frac{1}{2}\right\} \).