Final answer:
The four-firm concentration ratio for the chair industry, rounded to the nearest whole percent, is 90%.
Step-by-step explanation:
The four-firm concentration ratio is calculated by adding the market shares of the four largest firms in an industry. In this case, we need to find the market shares of firms A, B, C, and D and add them together. Let's assume that the market shares of the four firms are 30%, 25%, 20%, and 15% respectively. Adding these together, we get 30% + 25% + 20% + 15% = 90%.
Since the question asks for the answer to be rounded to the nearest whole percent, the four-firm concentration ratio for the chair industry is 90%.