Chapter 5 - Continuous Random Variables - Exercises 5.20 - 5.52 - Learning the Mechanics - Page 242: 5.32c

$x=40.24$

$p(z\gt z_0)=.10$ $p(0\lt z\lt z_0)=p(z\gt0)-p(z\gt z_0)=.5-.1=.4$ According to Table IV, page 773: If $p(0\lt z\lt z_0)=.4$ then $z_0\approx1.28$ $z_0=\frac{x-\mu}{\sigma}$ $1.28=\frac{x-30}{8}$ $x-30=1.28(8)$ $x=30+10.24=40.24$