Answer
$x=325.2$
$x=338.4$
Work Step by Step
According to table IV, page 773:
$p(0\lt z\lt .84)=.3$
$p(z\lt.84)=p(z\leq0)+p(0\lt z\lt .84)=.5+.3=.80$
$z_0=\frac{x-\mu}{\sigma}$
$.84=\frac{x-300}{30}$
$x-300=25.2$
$x=325.2$
According to table IV, page 773:
$p(0\lt z\lt 1.28)=.4$
$p(z\lt1.28)=p(z\leq0)+p(0\lt z\lt1.28)=.5+.4=.9$
$p(z\lt-1.28)=1-p(z\gt-1.28)=1-p(z\lt1.28)=1-.9=.10$
$z_0=\frac{x-\mu}{\sigma}$
$-1.28=\frac{x-300}{30}$
$x-300=38.4$
$x=338.4$
