Answer
$8.805cm$
Work Step by Step
Given $\mu=8,3,\sigma=0.6$, assume the minimum thickness of the oversized
books on the library shelf is $X_0$, we have $z=\frac{X_0-8.3}{0.6}$
We were given that $P(X\gt X_0)=1-P(z)=0.2$, we have $P(z)=0.8$ and use Table E
or a calculator, we can find $z=0.8416$. Thus $\frac{X_0-8.3}{0.6}=0.8416$ and
$X_0=8.805cm$
