Suppose a monopoly concrete contractor builds 20 driveways per month for $10,000 each. In order to increase sales to 21 driveways, the contractor must lower the price of driveways to $9,500. The marginal revenue of the 21st driveway is

Answer: Marginal revenue is - $500.

Explanation: The marginal revenue is calculated as the change in total revenue subtracted by the change in quantity.

Total revenue is calculated by multiplying the price by the quantity:

At a quantity of 20 driveways, the total revenue is = 20 * $10,000 = $200,000

At a quantity of 21 driveways, the total revenue is = 21 * $9,500 = $199,500

Marginal revenue = $199,500 - $200,000

= - $500