曼昆经济学原理生产成本.ppt

* * In this example, the efficient scale is Q=5, where ATC = $76. At any Q below or above 5, ATC $76. * * The textbook gives a nice analogy to help students understand this. A student’s GPA is like ATC. The grade she earns in her next course is like MC. If her next grade (MC) is less than her GPA (ATC), then her GPA will fall. If her next grade (MC) is greater than her GPA (ATC), then her GPA will rise. I suggest letting students read the GPA example in the book and giving them the following example in class: You run a pizza joint. You’re producing 100 pizzas per night, and your cost per pizza (ATC) is $3. The cost of producing one more pizza (MC) is $2. If you produce this pizza, what happens to ATC? Most students will understand immediately that ATC falls (albeit by a small amount). Instead, suppose the cost of producing one more pizza (MC) is $4. Then, producing this additional pizza causes ATC to rise. * * The following might be helpful: After the first paragraph displays, pick a Q a little to the left of QA. From this Q, go up to the ATC curves. Notice that cost per unit is lower for the small factory than the medium one. The firm may be stuck with a medium factory in the short run, but in the long run – if it wishes to produce this level of output – it will choose the small factory to have the lowest cost per unit. Hence, for Q QA, the LRATC curve is the portion of ATCS from 0 to QA. After the second paragraph displays, pick a Q a little to the right of QA. From this Q, go up to the ATC curves. Notice that cost per unit is lower for the medium factory than the small one. The firm may be stuck with a small factory in the short run, but in the long run – if it wishes to produce this level of output – it will choose the medium factory to have the lowest cost per unit. Hence, for QA Q QB, the LRATC curve is the portion of ATCM from QB to QA. The same type of argument illustrates the logic in the third paragraph. * * This s