Answer:
a. Four-firm concentration ratio is the total sales percentage of the top 4 burger shops in the industry;
= 25% + 24% + 18% + 12%
= 79%
b. Herfindahl index is the sum of the squares of the percentage sales of all the shops in the industry;
= 25² + 24² + 18² + 12² + 11² + 6² + 4²
= 1,842
c. Top 3 shops combine to form one shop.
= 25 + 24 + 18
= 67%
Four-firm ratio = 67% + 12% + 11% + 6%
= 96%
Herfindahl index = 67² + 12² + 11² + 6² + 4²
= 4,806
