Question

Given the total cost TC = 3q²+7q+12, evaluate the marginal cost and average cost if q = 3

Answer 1

TC(q) = 3 q² + 7 q + 12
Average cost = TC(q) / q = 3 q + 7 + 12/q

Average cost for a quantity produced q= 3 is : 3*3+7+ 12/3 = 20 units

TC(q-1) = 3 (q-1)² + 7 (q-1) + 12
Marginal cost = TC(q) - TC(q-1)
  = 6 q + 4 

For a quantity of q = 3, produced, the marginal cost is 6*3+4 = 22.