If a firm sells 5 units of output at $9 per unit and 6 units of output when price is reduced to $8, its marginal revenue from selling the sixth unit is

Diamonds are nature's hardest substance. Classify each of the following diamonds as land, labor, capital, entrepreneurship, or none of the above. Explain your choice.

a . an unmined diamond b. a diamond in DeBeers' vault (DeBeers is the world's biggest diamond mining company.) c. a diamond in a jeweler's display case at the shopping mall d. a diamond on your or your fiancée's finger e. an industrial-grade diamond in your dentist's drill f. the diamonds in the blade that the highway department uses to cut concrete

Which would concern you most, a 5 percent increase in concentration in a market where the four-firm concentration ratio is 3 percent, 42 percent or 85 percent? Explain your reasoning