1. If an industry is formed by six companies. Four companies have sales of $ 10 each, and two companies have sales of $ 5 each.
a. What is the concentration ratio of four companies for this industry? and what does it mean?
b. What is the Herfindahl-Hirschman index for this industry?
c. Explain the differences that occur from calculations with concentrations of 4 companies compared to calculations with HHI?

Please explain it thoroughly, Thankyou so much in advance!