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Numerical Problems · Q10

Q.A monopolist faces the demand curve P=20−QP = 20 - Q and has a constant marginal cost of MC=4MC = 4. Find the profit-maximising output and price.

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The demand (AR) curve is P=20−QP = 20 - Q, so total revenue is

TR=P×Q=(20−Q)Q=20Q−Q2.TR = P \times Q = (20 - Q)Q = 20Q - Q^{2}.

Marginal revenue is the rate of change of TR with output:

MR=20−2Q.MR = 20 - 2Q.

The monopolist maximises profit where MR=MCMR = MC:

20−2Q=4⇒2Q=16⇒Q=8.20 - 2Q = 4 \Rightarrow 2Q = 16 \Rightarrow Q = 8.

Price is read from the demand (AR) curve at this output:

P=20−Q=20−8=12.P = 20 - Q = 20 - 8 = 12. …

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