Originally Posted by **CaptainBlack**

b)The marginal cost of production when production is at $\displaystyle N$ units is the

additional cost of producing the $\displaystyle N+1$ th unit (check the definition you have

been given to see if it agrees with this). So here the marginal cost is $\displaystyle 10$ units of cost.

But that is not what the question asks for, it asks for the marginal avaerage cost

[Math]MAC(n)[/tex], which is a term which is unfamilliar to me, but I will assume this means

the change in average cost of producing one more item:

$\displaystyle

MAC(n)=AC(n+1)-AC(n)=$$\displaystyle \frac{10(n+1)+3000}{n+1} - \frac{10n+3000}{n}=\frac{3000}{n(n+1)}

$