想請問兩條關於微積分的mc

If the average cost per Unit C(X) to produce X units of plywood is given by C(X)=900/(X-30), what do 600 units cost?
A. $180.00
B. $857.14
C. $18,000
D. $899.95

The answer is B.
(In the question, it should be C(X) = 900/(X+30) instead.)

When X = 600,
Total cost for 600 units
= $C(600) x 600
= $[900/(600 + 30)] x 600
= $857.14


Suppose a cost-benefit model is given by Y=6.3X/(100-X), where Y is the cost in thousands of dollars for removing X percent of a given pollutant. Find the cost of removing 45% to the nearest dollars.
A. $5155
B. $818
C. $2835
D. $6300

The answer is A.

When X = 45,
Total cost
= $Y x 1000
= $[6.3(45)/(100 - 45)] x 1000
= $5155