Suppose the Average Costs of a Mining Operation Depend on the Number

Multiple Choice

Suppose the average costs of a mining operation depend on the number of machines used, and average costs, in dollars, are given by , , where x is the number of machines used. How many machines give minimum average costs? ​

A) Using 25 machines gives the minimum average costs.
B) Using zero machines gives the minimum average costs.
C) Using 35 machines gives the minimum average costs.
D) Using 50 machines gives the minimum average costs.
E) Using 55 machines gives the minimum average costs.