Chapter 5 - Continuous Random Variables - Exercises 5.20 - 5.52 - Applying the Concepts - Basic - Page 243: 5.41b

$p(40\lt x\lt60)=.7528$

$z=\frac{x-\mu}{\sigma}=\frac{60-48.5}{8.5}=1.35$ $z=\frac{x-\mu}{\sigma}=\frac{40-48.5}{8.5}=-1$ According to table IV, page 773: $p(0\lt z\lt1)=.3413$ $p(0\lt z\lt 1.35)=.0948$ $p(40\lt x\lt60)=p(-1\lt z\lt1.35)=p(-1\lt z\lt0)+p(0\lt z\lt1.35)=p(0\lt z\lt1)+p(0\lt z\lt1.35)=.3413+.4115=.7528$