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Theory of the Firm in Perfect Competition Two Critical Decisions; Long Run vs Short Run; Widget Production

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The Firms Problem Maximize profit: n Given available technology: Q(K,L) n Given prices of inputs: w and r n Given price of final good Q

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Two Critical Decisions n How to produce? –List technically efficient methods –Choose the lowest cost method: L*,K* –TC(Q)=wL*+rK* n How much to produce? –Profit = Total Revenue-Total Costs –Total Revenue=PQ –Total Costs=TC(Q)

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Total Revenue-Total Cost

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Profit

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Profit Maximization Rule

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Some Basic Vocabulary n Explicit costs vs Implicit costs –Explicit costs require an outlay of money by firm; Implicit costs do not. n Economic Profit vs Accounting profit –Economists include opportunity costs in calculating economic profit; Accountants do not. n Long run vs short run –In long run both K and L are variable. In short run, K is fixed Only L is variable.

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Short Run Production n Widget manufacturing –Variable Input -- Labor (Staples) –Fixed Inputs -- Table, Stapler n Production Table –Total Product -- total number of widgets –Average Product -- total number of widgets divided by total number of workers –Marginal Product -- change in number of widgets following addition of worker

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Discussion n What happens to marginal product as number of workers increases? n What happens to total costs as number of workers increases? n What happens to cost per unit produced as output increases?

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Short Run Costs n Fixed vs variable costs n ATC=Total Cost/Output n AVC=Total Variable Cost/Output n AFC=Total Fixed Cost/Output MC = TC/ Q –Change in Total Cost associated with last unit produced

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Typical Short Run Cost Curves

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Marginal Cost n Marginal cost is inversely related to marginal product. n Because of the law of diminishing marginal returns (diminishing marginal productivity), short run marginal cost slopes up. Why is that important? n Marginal cost will intersect AC at minimum of AC.

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Long Run Production n Plans Output (Q) n Firm chooses K and L to produce Q at lowest possible cost n Chooses among technically efficient technologies (combinations of K &L)

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Technically Efficient Technologies: Q=20

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Cost Minimizing Technology? w=$5 and r=$10

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Long Run Production

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Long Run Total Costs

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Returns to Scale n Increasing Returns to Scale –As inputs double, output more than doubles –Average total costs are decreasing n Constant Returns to Scale –As inputs double, output doubles –Average total costs are constant n Decreasing Returns to Scale –As inputs double, output less than doubles –Average total costs are increasing

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Relationship between Long Run and Short Run Costs n Short run, K is fixed. Only L variable n Suppose firm built factory with K=2, anticipating production of 40 units. n If output is 20 instead, firm will have total costs of $30 and SRATC of $15. SRATC would be greater than LRATC.

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Relationship between Long Run and Short Run Costs

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Summary n For economists, cost is opportunity cost. It includes the opportunity cost of capital invested in firm. n In long run firms choose K and L to produce planned output at lowest cost. n Short run production is characterized by diminishing marginal returns. n MC will intersect ATC at ATCs minimum. n Minimums of SRATCs will be tangent to LRATC

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