The market for radios consists of 100consumers, each ofwhom has the demand function: QDradio = 4 − 0.4 Pradio+ 0.0025 Income +0.25 Pnewspaper − 0.005 Pbatteries At current average prices, a radio costs Â￡10, anewspapercosts Â￡1, and batteries cost Â￡2. Average income isÂ￡1,000. The market demandcurve for radios is most accuratelydescribed as:
A) 400 − 40 Pradio + 0.25 Income +    25 Pnewspaper − 0.5 Pbatteries.  
B) 16.85 − 0.025 QDradio.  
C) 674 − 40 Pradio.
        答案 B
 
Aggregating the individual demand functionsinto the marketdemand function we get:
QDradio = 100(4 − 0.4 Pradio + 0.0025Income +0.25 Pnewspaper − 0.005 Pbatteries)
QDradio = 400 − 40 Pradio + 0.25 Income +25Pnewspaper − 0.5 Pbatteries
Substituting average values for all variablesexcept pricewe get:
QDradio = 400 − 40 Pradio + 0.25(1,000)+25(1) − 0.5(2)
QDradio = 400 − 40 Pradio + 250 + 25 − 1
QDradio = 674 − 40 Pradio
40 Pradio = 674 − QDradio
Solving for price gives us the demandcurve:
Pradio = 16.85 − 0.025 QDradio

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