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

$p(x\gt40)=.9406$

$z=\frac{x-\mu}{\sigma}=\frac{40-50}{6.4}=-1.56$ According to table IV, page 773: $p(0\lt z\lt1.56)=.4406$ $p(x\gt40)=p(z\gt-1.56)=p(-1.56\lt z\lt0)+p(z\gt0)=p(0\lt z\lt1.56)+p(z\gt0)=.4406+.5=.9406$