The Herfindahl index is 2500.
An oligopolistic industry is an industry where there are few large firms operating in the industry. This is because there are relatively high barriers to entry. The firms set the price in an oligopolistic industry.
The four-firm concentration ratio calculates the concentration ratio of the 4 largest firms in an industry.
The concentration ratio of each firm = 100% / 4 = 25%
The Herfindahl index is calculated by squaring the market share of each firm in the industry.
4 x (25²) = 2500
For more information about concentration ratio, please check : https://brainly.com/question/9430331
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