Answer: B. In the short run, the typical firm increases its output and makes an above normal profit.
Step-by-step explanation:
I have attached a graph to explain.
Originally the Perfectly Competitive Market is in a long run Equilibrium.
This means that at 5000 units the $20 selling price was as a result of Marginal Revenue being equal to Marginal Cost.
Now a sudden change in Demand has taken the price up which then forces the Marginal Revenue Curve upwards.
This will culminate with the Marginal Revenue Curve now intersecting the Marginal Cost curve at a higher point being point F so that profit can be maximised.
This higher level will thus lead to a higher output than 5000 units at point Q as the firm will increase output.
Notice that at that point the Marginal Revenue is higher than Average Total Cost meaning that an Above normal profit is being made.
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