There are five firms in an industry. You know sales of the four largest firms are $800,000, $700,000, $440,000, and $230,000. If the C4 rati

First, find the sales of the fifth firm.

Sum of the first four firms is  $2,170,000  and this represents  80%  of the market.

Letting X represent the total market, and writing 80% as .80:

Thus:  .80 · X  =  2,170,000     --->   X  =  2, 712, 500

The fifth firm therefore has value:  2,712,500 - 2,170,000  =  542,000

To find the index, sum the square  of each of the percentages:  

    800 000 / 2 712 500  =  29.5%

    700 000 / 2 712 500  =  25.8%

    440 000 / 2 712 500  =  16.2%

    230 000 / 2 712 500  =    8.5%

    542 000 / 2 712 500  =  20.0%

Index  =  (.295)² + (.258)² + (.162)² + (.085)² + (.200)²  =  0.227

4 firms control market for certain good. HHI = 2900. Total Industry sale = $500. @ firms have $175 sales each. If other 2 firms have same sales, what is their market share? Any help will be gratifying!