A company's revenue from car sales, C (in thousands of dollars), is a function of advertising expenditure, a, in thousands of dollars, so C = f(a).

(a) What does the company hope is true about the sign of f'?

(b) What does the statement f'(100) = 2 mean in practical terms? How about f'(100) = 0:5?

(c) Suppose the company plans to spend about $100; 000 on advertising. If f'(100) = 2, should the

company spend more or less than $100,000 on advertising? What if f'(100) = 0:5?