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Marginal revenue and marginal cost for the healthpill monopoly

The graph shows marginal cost as an upward-sloping curve and marginal revenue as a downward-sloping line. Where the two lines intersect is where maximum profit is possible.
For a monopoly like HealthPill, marginal revenue decreases as additional units are sold. The marginal cost curve is upward-sloping. The profit-maximizing choice for the monopoly will be to produce at the quantity where marginal revenue is equal to marginal cost: that is, MR = MC. If the monopoly produces a lower quantity, then MR>MC at those levels of output, and the firm can make higher profits by expanding output. If the firm produces at a greater quantity, then MC>MR, and the firm can make higher profits by reducing its quantity of output.
Costs and revenues of healthpill
Cost Information Revenue Information
Quantity Total Cost Marginal Cost Average Cost Quantity Price Total Revenue Marginal Revenue
1 1,500 1,500 1,500 1 1,200 1,200 1,200
2 1,800 300 900 2 1,100 2,200 1,000
3 2,200 400 733 3 1,000 3,000 800
4 2,800 600 700 4 900 3,600 600
5 3,500 700 700 5 800 4,000 400
6 4,200 700 700 6 700 4,200 200
7 5,600 1,400 800 7 600 4,200 0
8 7,400 1,800 925 8 500 4,000 –200

A monopolist can determine its profit-maximizing price and quantity by analyzing the marginal revenue and marginal costs of producing an extra unit. If the marginal revenue exceeds the marginal cost, then the firm should produce the extra unit.

For example, at an output of 3 in [link] , marginal revenue is 800 and marginal cost is 400, so producing this unit will clearly add to overall profits. At an output of 4, marginal revenue is 600 and marginal cost is 600, so producing this unit still means overall profits are unchanged. However, expanding output from 4 to 5 would involve a marginal revenue of 400 and a marginal cost of 700, so that fifth unit would actually reduce profits. Thus, the monopoly can tell from the marginal revenue and marginal cost that of the choices given in the table, the profit-maximizing level of output is 4.

Indeed, the monopoly could seek out the profit-maximizing level of output by increasing quantity by a small amount, calculating marginal revenue and marginal cost, and then either increasing output as long as marginal revenue exceeds marginal cost or reducing output if marginal cost exceeds marginal revenue. This process works without any need to calculate total revenue and total cost. Thus, a profit-maximizing monopoly should follow the rule of producing up to the quantity where marginal revenue is equal to marginal cost—that is, MR = MC.

Maximizing profits

If you find it counterintuitive that producing where marginal revenue equals marginal cost will maximize profits, working through the numbers will help.

Step 1. Remember that marginal cost is defined as the change in total cost from producing a small amount of additional output.

MC = change in total cost change in quantity produced

Step 2. Note that in [link] , as output increases from 1 to 2 units, total cost increases from $1500 to $1800. As a result, the marginal cost of the second unit will be:

MC = $1800 $1500 1 = $300

Step 3. Remember that, similarly, marginal revenue is the change in total revenue from selling a small amount of additional output.

MR = change in total revenue change in quantity sold

Step 4. Note that in [link] , as output increases from 1 to 2 units, total revenue increases from $1200 to $2200. As a result, the marginal revenue of the second unit will be:

MR = $2200 $1200 1 = $1000

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Source:  OpenStax, Openstax microeconomics in ten weeks. OpenStax CNX. Sep 03, 2014 Download for free at http://legacy.cnx.org/content/col11703/1.2
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