Chapter 2.5, Problem 91E

Advertising. A marine manufacturer will sell N(x) power boats after spending $x thousand on advertising, as given by

$N(x)=1,000-\frac{3,780}{x}5\le x\le 30$

(see figure).

1. (A)   Find N′(x).
2. (B)   Find N′(10) and N′(20). Write a brief verbal interpretation of these results.