Question 1021069:  cost of producing x cars per week is C(x)=1000+400x-0.1x^2 
what is the cost of producing 301 cars? 
 Answer by robertb(5830)      (Show Source): 
You can  put this solution on YOUR website! First, I will understand this problem as a follow up to your previous question of finding the marginal cost at x = 300, and second, what you're actually trying to ask is what is the approximate cost of producing the 301st car, which the marginal cost precisely estimates. 
With that in mind, the extra cost in manufacturing the 301st car is approximately $340.  Normally this would be computed as C(301) - C(300), whose exact value is $339.90.  As you can see the marginal cost value of $340 at x = 300 gives a pretty good estimate.  
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