EX 4.15

$z_{.05}$ is the $100\left(1-.05\right)$ th $=95$ th percentile of the standard normal distribution, so $z_{.05}=1.645$. The area under the standard normal curve to the left of $-z_{.05}$ is also .05. (See Figure 4.20.)

Figure 4.20 Finding $z_{.05}$