Sprint is one of the largest mobile service providers in the USA. In March 2011, Sprint had 13.1 million prepaid customers, and 33 million post-paid customers. Sprint's prepaid brands include Virgin Mobile USA, Boost Mobile, and Assurance Wireless. Sprint's ARPU from prepaid customers was $28 per month, as compared with $56 per month from post-paid customers.

(a) Explain the meaning of normal and inferior products.

(b) Apply the concepts of normal and inferior products to prepaid and post-paid mobile telephone service.

(c) Refer to Sprint's ARPU from prepaid and post-paid customers. Are the data consistent with your answer to (b)?