1. Microeconomics 2 John Hey

2. Plan for today 1.We look at the Homework I set at the end of Lecture 11. 2.We will quickly revise the relationships between the total, average and marginal cost curves. 3.We look at the optimal supply (“how much?”) decision of the competitive firm (one who takes all prices as given). 4.We will show that the supply curve is the marginal cost curve (if upward sloping) and... 5.... that the firms’ profit is the area between the supply curve and the price of output. (which is the parallel of the result for the consumer surplus)

3. Homework CES technology with parameters c 1 =0.4, c 2 =0.5, ρ=0.9 and s=1.0. (Note: constant returns to scale.) The production function: y = ((0.4q 1 -0.9 )+(0.5q 2 -0.9 )) -1/0.9 I have inserted the isoquant for output = 40 (and also that for output = 60). I have inserted the lowest isocost at the prices w 1 = 1 and w 2 = 1 for the inputs. The optimal combination: q 1 = 33.38, q 2 = 37.54 and the cost = 33.58 + 37.54 = 70.92.

5. What you should do Find the optimal combination (either graphically or otherwise) and the (minimum) cost to produce the output for the following: w 1 = 2 w 2 = 1 y=40 w 1 = 3 w 2 = 1 y=40 w 1 = 1 w 2 = 1 y=60 w 1 = 2 w 2 = 1 y=60 w 1 = 3 w 2 = 1 y=60 Put the results in a table.

6. You can do this graphically or algebraically Algebraically The formulae (in the Maple file) are: q 1 =y 1/s (c 1 /w 1 ) 1/(1+ρ) [(c 1 w 1 ρ ) 1/(1+ρ) ) +(c 2 w 2 ρ ) 1/(1+ρ) ] 1/ρ q 2 =y 1/s (c 2 /w 2 ) 1/(1+ρ) [(c 1 w 1 ρ ) 1/(1+ρ) ) +(c 2 w 2 ρ ) 1/(1+ρ) ] 1/ρ where y is the desired output.

9. Results yw1w1 w2w2 q1q1 q2q2 cost 401133.437.570.9 402127.945.2101.1 403125.551.2127.7 601150.156.3106.4 602141.967.9151.7 603138.376.7191.6

10. Chapter 12 The total cost C(y) is the minimum cost to produce a given level of output y. It is always upward-sloping (in the long period passes through the origin) and its shape depends upon the returns to scale: decreasing ↔ convex constant ↔ linear increasing ↔ concave

11. Chapter 12 The total cost C(y) is the minimum cost to produce a given level of output y. The average cost, C(y)/y, is the slope of the line from the origin to the total cost curve. The marginal cost, the rate at which total cost increases with output, is equal to the slope of the total cost curve.

12. Constant returns to scale: total cost

13. Constant returns to scale: marginal and average costs

14. Total cost: decreasing returns to scale

15. Two examples (of average and marginal costs) with decreasing returns

16. Average cost at an output of 40

17. Average cost at the output of 80

18. The average cost curve

19. Marginal cost at the output 40

20. Marginal cost at the output 80

21. The marginal cost curve

22. From the total cost curve to the marginal cost curve and back. The marginal cost curve is the slope of the total cost curve...... hence the total cost curve is the area under the marginal cost curve. The marginal cost curve is the derivative of the total cost curve...... hence the total cost curve is the integral of the marginal cost curve.

23. Chapter 13 Today we find the optimal output for a perfectly competitive firm......that takes the price of its output as given. We will assume to begin with that the firm has decreasing returns to scale. We will see later that there are problems if the firm has increasing or constant returns to scale. Let us go to the Maple html file...... in which we assume to begin with that the output price is 30 (per unit).

24. Chapter 13: summary The condition for the optimal output: price = marginal cost...... where marginal cost is rising. It follows that the supply curve of the firm is simply its marginal cost curve. The profit/surplus of the firm is the area between the price and its supply curve.

25. Chapter 13 Goodbye!