Chapter 5 - Continuous Random Variables - Exercises 5.20 - 5.52 - Applying the Concepts - Basic - Page 242: 5.39a

$p(55\lt x\lt60)=.1583$

$z=\frac{x-\mu}{\sigma}=\frac{55-50}{6.4}=.78$ $z=\frac{x-\mu}{\sigma}=\frac{60-50}{6.4}=1.56$ According to table IV, page 773: $p(0\lt z\lt .78)=.2823$ $p(0\lt z\lt1.56)=.4406$ $p(55\lt x\lt60)=p(.78\lt z\lt1.56)=p(0\lt z\lt 1.56)-p(0\lt z\lt .78)=.4406-.2823=.1583$