Sprint is one of the largest mobile service providers in the USA. In March 2011, Sprint had 13.1 million pre-paid customers, and 33 million post-paid customers. Sprint's Average Revenue Per Unit from pre-paid customers was $28 per month, as compared with $56 per month from post-paid customers. (a) Explain the meaning of normal and inferior products. Are the pre and post-paid services normal necessities, normal luxuries or inferior services (b) Apply the concepts of normal and inferior products services to pre-paid and post-paid mobile telephone service and what are the implications for its markets. (c) Refer to Sprint's ARPU from pre-paid and post-paid customers. Are the data consistent with your answer to (b) and how does growth in market sales effect its ARPU and why