Suppose that De Beers is a single-price monopolist in the diamond market. De
Beers has five potential customers:
Raquel, Jackie, Joan, Mia, and Sophia. Each of these customers will buy at
most one diamond-and only if the price is just equal to, or lower than, her
willingness to pay. Raquel's willingness to pay is \(\$ 400 ;\) Jackie's, \$300;
Joan's, \$200; Mia's, \$100; and Sophia's, \$0. De Beers's marginal cost per
diamond is \(\$ 100 .\) The result is a demand schedule for diamonds as follows:
$$\begin{array}{c|c}
\begin{array}{c}\text { Price of } \\\\\text { diamond }\end{array} &
\begin{array}{c}\text { Quantity of diamonds } \\
\text { demanded }\end{array} \\\\\ 500 & 0 \\\400 & 1 \\\300 & 2 \\\200 & 3
\\\100 & 4 \\\0 & 5\end{array}$$
a. Calculate De Beers's total revenue and its marginal revenue. From your
calculation, draw the demand curve and the marginal revenue curve.
b. Explain why De Beers faces a downward-sloping demand curve and why the
marginal revenue from an additional diamond sale is less than the price of the
diamond.
c. Suppose De Beers currently charges \(\$ 200\) for its diamonds. If it lowers
the price to \(\$ 100\), how large is the price effect? How large is the
quantity effect?
d. Add the marginal cost curve to your diagram from part a and determine which
quantity maximizes De Beers's profit and which price De Beers will charge.