A market research consultant hired by the Pepsi-Cola Co. is interested in determining the proportion of consumers who favor Pepsi-Cola over Coke Classic in a particular urban location. A frame of customers from the market under investigation is provided in P8_44.XLS. 

a. What sample size would be required for the market research consultant to be approximately 95% sure that her estimate of the proportion of consumers who favor Pepsi-Cola in the given urban location is within 0.20 of the true proportion? Assume that her best estimate of the population proportion parameter p is 0.45. 

b How does the answer to part a change if the market research consultant wants her estimate to be within 0.15 of the actual population proportion? Explain the difference in your answers to parts a and b.