1. Consider data on U.S. Refrigerator sales from 2009. The market shares of the top 4 firms was 12% for Sears, 9% for Lowes, 5% for Walmart, and 3.5% for Home Depot. Firms 5 through 25 combined summed to 20.5%m and all other independents outside the top 25 selling firms comprised the other 50% of industry sales.
What is the 4-firm concentration ratio for this industry?