Chapter 2.6, Problem 47E

Use differential approximations in the following problems.

47. Average cost. For a company that manufactures tennis rackets, the average cost per racket $\bar{C}$ is

$\bar{C}=\frac{400}{x}+5+\frac{1}{2}xx\ge 1$

where x is the number of rackets produced per hour. What will the approximate change in average cost per racket be if production is increased from 20 per hour to 25 per hour? From 40 per hour to 45 per hour?