Sales of Amazon's reader, the Kindle, are projected to reach 4 million by Christmas, 2011. Amazon has 630,000 ebooks available for sale with approximately 510,000 books priced at less than $10. Currently ebooks outsell the traditional hardback and paperback by a ration of 1.5 to 1. As the price of the Kindle has fallen from $234 to $134, the number of ebooks sold have increased. Economics would define the behavior of ebooks as a "complementary good."
A complementary good goes along with another good such as cookies and milk or gasoline and a automobile. When the price of one good decreases, the demand for the complement increases like the ebooks.
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