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

$p(48\lt x\lt52)=.2434$

$z=\frac{x-\mu}{\sigma}=\frac{48-50}{6.4}=-.31$ $z=\frac{x-\mu}{\sigma}=\frac{52-50}{6.4}=.31$ According to table IV, page 773: $p(0\lt z\lt .31)=.1217$ $p(48\lt x\lt52)=p(-.31\lt z\lt.31)=2p(0\lt z\lt .31)=2(.1217)=.2434$