The following 16 questions cover some of the material that is relevant for the third exam.

The exact questions given below will not be on the exam. Questions that are similar to (at least) some of them will be. Understanding the answers to these questions will therefore help you prepare for the exam.

Answers and explanations for all 16 questions are found at the bottom of this page. The link after each question takes you to the relevant answer. Please note that while checking the answer to question 3 (for example), you may also be able to see the answer to question 4. If you prefer not to see an answer before you've read the corresponding question, you may wish to look over all the questions before checking any answers.

Please note that studying for the third exam should entail more than merely reviewing this page. The exam itself has 17 questions, and while these sample questions cover some of what we've done in class, there will certainly be topics appearing on the exam that do not appear in these example questions. Make sure to also study your class notes and the homework questions, and read the material on the (web-page) outside reading list.

1. Complete the following statement. If a firm sells the quantity of output at which its marginal revenue _____, then that firm can be absolutely certain that its total revenue _____.   [answer and explanation]
   1. equals its marginal cost   ;   exceeds its total cost by the largest possible amount
   2. equals its marginal cost   ;   equals its total cost
   3. exceeds its marginal cost by the largest possible amount   ;   exceeds its total cost by the largest possible amount
   4. exceeds its marginal cost by the largest possible amount   ;   equals its total cost
   5. Both (a) and (d) are correct.

2. We know that when Firm XYZ produces and sells 20 units of its product, it earns a larger profit than it would earn if it produced and sold 19 units, or 21 units, or any other quantity. From this fact, we know that the following statement must also be true. The marginal revenue that Firm XYZ receives as a result of selling the 20th unit must _____.   [answer and explanation]
   1. exceed the marginal cost of producing the 20th unit by more than MR exceeds MC for any other unit that XYZ produces
   2. be less than the marginal cost of producing the 20th unit by a greater amount than MR is less than MC for any other unit that XYZ produces
   3. exceed (or be equal to) the marginal cost of producing the 20th unit, while the MR from the 21st unit must be less than the MC of that unit
   4. be less than (or be equal to) the marginal cost of producing the 20th unit, while the MR from the 21st unit must exceed the MC of that unit
   5. equal zero

3. Quantity	Total Cost
   1	$37
   2	$45
   3	$55
   4	$68
   5	$86
   6	$111
   7	$145

   Betty owns a firm, and that firm's total cost of producing various quantities of output are given in the table. If Betty can sell as many units of this output as she wishes at an unchanging price of $20 per unit, Betty would maximize her profits by selling _____ units.   [answer and explanation]
   1. 3
   2. 4
   3. 5
   4. 6
   5. 7

4. Regardless of the number of days on which he opens his store, Frank pays a set amount of $1200 per month (for an average cost of $40 per day) to rent the building in which his store is located. Frank is committed to making this payment. Frank doesn't actually work at the store, but he does decide what its hours of operation will be. For every day that Frank opens the store, he must both pay wages to his employees and pay for electricity. These costs add up to $100 per day. If Frank decides to open his store on Sunday, the store will collect $300 in revenue; the items it sells that day cost $180 to buy. Frank's business is generally profitable, but he is trying to decide whether to stay open or close down on Sunday. Assume that whether he opens or closes on Sunday has no effect on the store's sales on other days. Given the above numbers, if Frank decides to keep his store open on Sunday, the result will be that his store's total profit will _____.   [answer and explanation]
   1. rise
   2. fall
   3. remain unchanged
   4. definitely fall to zero

5. A firm sells 300 units of its output at a per-unit price of $10. The firm's marginal cost of producing its 300th unit also equals $10. If the firm's output were to rise above 300 units, its marginal cost would slowly rise above $10. The firm's average total cost of production (when 300 units are produced) equals $8. Based on this information, we know that this firm _____.   [answer and explanation]
   1. would (in the short run) definitely raise its profit by increasing production from 300 to 310 units
   2. is currently earning a (total) profit that is greater than $500
   3. is currently earning a (total) profit that is less than $500
   4. Both (a) and (b) are correct.
   5. Both (a) and (c) are correct.

   

6. The accompanying figure illustrates the situation facing one firm in a competitive market. Each of the small marks on the vertical axis measures $1; some values on the horizontal axis are marked. When this firm produces the quantity of output that maximizes its profit, the information in the graph indicates that its (total) profit equals _____.   [answer and explanation]
   1. 88
   2. 90
   3. 120
   4. 352
   5. 480

7. Suppose that firms originally active in a competitive market are earning positive economic profits. As a result, the number of firms participating in the market will, over time, change. This change causes (i) the quantity produced in the market to move _____ the economically efficient (economic-surplus-maximizing) quantity of output, and (ii) causes _____ in the profits earned by the original firms.   [answer and explanation]
   1. farther from  ;  an increase
   2. farther from  ;  a decrease
   3. closer to  ;  an increase
   4. closer to  ;  a decrease

8. For this question, assume that the long-run supply curve for a given good is upward-sloping. That curve is _____ than is the short-run supply curve for the same good. Assume that the market for the good is originally in a long-run equilibrium, and that there is an unexpected (and long-lasting) increase in the demand for the product. In response to the demand increase, the market price of the relevant good will rise in the short run, and then (assuming no other shifts in demand, or changes in production cost, occur) will _____ as time passes and the market moves into a long run situation.   [answer and explanation]
   1. flatter   ;   fall back towards the original price
   2. flatter   ;   again rise
   3. steeper   ;   fall back towards the original price
   4. steeper   ;   again rise
   5. steeper   ;   stay unchanged

9. Tou's Company is currently (on a daily basis) selling 40 units of its product at a price of $30 per unit. In order to increase its sales to 41 units, Tou's must reduce the price it charges (all its customers) by 25 cents. If Tou's Company increases its sales from 40 units to 41 units, the marginal revenue it collects as a result will _____.   [answer and explanation]
   1. equal exactly $30
   2. equal exactly $29.75
   3. fall somewhere in the range between $26.00 and $29.75
   4. fall somewhere in the range between $22.00 and $26.00
   5. fall somewhere in the range between $18.00 and $22.00

10. Suppose that a certain market has all the characteristics of monopolistic competition. Which of the following statements about such a market is correct?
    (i) All firms in the market have perfectly horizontal firm demand curves.
    (ii) When the existing firms are earning economic profits, they can prevent new firms from entering the market.
    (iii) In a long-run equilibrium, the firms in the market are producing the good at the lowest cost that is technologically possible.   [answer and explanation]
    
    1. Only (i) is true.
    2. Only (ii) is true.
    3. Only (iii) is true.
    4. All of (i), (ii), and (iii) are true.
    5. None of (i), (ii), and (iii) is true.

11. Quantity	Price	Total Revenue
    1	60	60
    2	57	114
    3	54	162
    4	51	204
    5	48	240
    6	45	270
    7	42	294
    8	39	312

    The accompanying table shows the price that a monopoly firm can charge (each of its customers) in order to sell a certain quantity of units. This firm can produce its product at a constant marginal cost of 40 per unit. Assume that this firm wishes to sell the quantity that maximizes its profit. To do this, the firm should charge a price of _____ per unit.   [answer and explanation]
    
    1. 54
    2. 51
    3. 48
    4. 45
    5. 42

12. Suppose that a firm is currently selling 8 units of its output at a price of $10 per unit. If the firm wishes to increase its sales to 9 units, it must lower the price it charges (to all its customers) by 50 cents. Suppose also that the firm's marginal cost of producing the 9th unit equal $7. [When answering this question ignore the possibility that a an externality cost (which we haven't yet covered) could exist.] In this case, we can be sure that producing and selling the 9th unit would _____.   [answer and explanation]
    
    1. increase this firm's profit
    2. decrease this firm's profit
    3. produce a net benefit for society; in other words, it would be efficient
    4. Both answers (a) and (c) are correct.
    5. Both answers (b) and (c) are correct.

13. Consider a market that is controlled by a monopoly firm (which charges the same price to all of its customers). Consider also the price-quantity combination that a profit-maximizing monopoly firm would choose. Suppose that for some reason (a profit-maximizing firm wouldn't do this voluntarily) the output produced by this firm rises. Such a change in output would cause the consumer surplus created in the market to _____, would cause the producer surplus created in the market to _____, and would cause the economic surplus created in the market to _____.   [answer and explanation]
    
    1. remain unchaged   ;   remain unchanged   ;   remain unchanged
    2. rise   ;   remain unchanged   ;   remain unchanged
    3. rise   ;   fall   ;   remain unchanged
    4. rise   ;   fall   ;   rise
    5. rise   ;   fall   ;   fall

14. Complete the following (unrelated) passages. (i) The (current or potential) existence of monopoly control over a market results in an inferior outcome when the relevant product _____ exist, but could result in a gain for society when the relevant product _____ exist. (ii) Consider a market-system economy, and focus on one particular market into which new firms are always able to enter. Suppose that there is an improvement in the industry's technology -- a rise in productivity -- that has the effect of lowering the average cost of production for all (current and potential) firms. In the long run, those that will probably most benefit from the rise in productivity are the _____ of the good.   [answer and explanation]
    
    1. does   ;   doesn't currently   ;   producers
    2. doesn't currently   ;   does   ;   producers
    3. does   ;   doesn't currently   ;   consumers
    4. doesn't currently   ;   does   ;   consumers

15. A certain firm is (to at least some extent) a price setter, and it sells its product in two different markets. The elasticity of demand for the firm's product in Market A is 3; the elasticity of demand for its product in Market B is 5. The firm's marginal cost of producing the product is the same no matter in which market it sells. Which of the following pricing strategies should this firm use in order to maximize its profit? It should charge _____.   [answer and explanation]
    
    1. a higher price in Market A
    2. a higher price in Market B
    3. the same price (but one above marginal cost) in both markets
    4. a price equal to marginal cost in both markets
    5. a price equal to zero in both markets

16. As in the previous question, assume that the elasticity of demand for a firm's product in a given market is 5. Assume also that the firm's Marginal Cost of producing its product is always $10. What price should the firm charge for its product in this market in order to maximize its profit?   [answer and explanation]
    
    1. $22.50
    2. $20
    3. $17.50
    4. $15.00
    5. $12.50

Question 1 answer is:   a.   equals its marginal cost   ;   exceeds its total cost by the largest possible amount

Explanation: This question shows the importance of understanding the difference between the meanings of marginal revenue and marginal cost and the meanings of total revenue and total cost.

Total revenue and total cost tell us how much, in total, the firm has received from selling a certain number of units of its product, and how much, in total, it cost to produce that number of units. Since profit equals total revenue minus total cost, a firm makes the largest profit it can possibly earn by selling the number of units for which total revenue exceeds total cost by the largest amount.

Marginal revenue and marginal cost tell us how total revenue and total cost change as a result of a change in the number of unit. More precisely, marginal revenue describes how total revenue changes when one more unit is sold, and marginal cost describes how total cost changes when one more unit is produced.

Because of the way profit is defined, saying that (producing and) selling one more unit increases a firm's profit is equivalent to saying that selling that unit increases the firm's total revenue by more than it increases its total cost.

Or, merely rephrasing the above, saying that selling one more unit increases a firm's profit is also equivalent to saying that selling that unit produces a marginal revenue that is larger than the marginal cost of producing it. Note that profit rises whenever MR exceeds MC, even if the difference between the two is only $1 (or 1 cent).

Furthermore, note that if a firm wants to maximize its profit, it should take advantage of any opportunity to sell a unit for which MR exceeds MC. Here's an example. Suppose the MR of unit 3 is $10 and the MR of unit 4 is $8, while the MC of unit 3 is $6 and the MC of unit 4 is $7. Selling the 3rd unit increases the firm's profit (since MR exceeds MC), and selling the 4th unit also increases the firm's profit (since MR exceeds MC). The rise is profit is bigger for the 3rd unit than it is for the 4th (because the difference between MR and MC is bigger for unit 3 than it is for unit 4), but both units produce a rise in profit.

A firm that wishes to maximize its profit thus should not stop selling at the point where MR exceeds MC by the largest amount (which is what answer (c) implies). Doing so means that the firm has missed an opportunity to increase its profit. In the example above, a firm that stopped when MR exceeded MC by the most would miss the chance to increase its profit (by only $1, but a dollar's a dollar) by selling the 4th unit.

Rather, a firm maximizes its profit (makes the difference between TR and TC as big as it can be) by selling every unit for which MR exceeds MC. This last statement is true regardless of whether MR exceeds MC by a lot, or only by a little.

Since the proper strategy for a firm that wants to maximize its profit is to sell every unit for which MR exceeds MC, the firm should continue to sell until the MR and MC of the last unit sold are equal (or as equal as possible) to each other.

Thus, by continuing to sell up to the point where MR equals MC, the firm guarantees that its TR exceeds it TC by the largest possible amount.

Question 2 answer is:   c.   exceed (or be equal to) the marginal cost of producing the 20th unit, while the MR from the 21st unit must be less than the MC of that unit

Explanation: The question tells us that when the first sells 20 units, it earns a bigger profit than it would earn if it sold 19 units, or 21 units, or any other quantity. In other words, the firm maximizes its profit by selling 20 units.

The above information tells us that when Firm XYZ increases its sales from 19 units to 20 units, its profit must rise, but when the firm increases its sales from 20 units to 21 units, its profit must fall. The first of these facts tells us that the firm's marginal revenue from selling its 20th unit must exceed its marginal cost of producing that unit (which is why selling unit #20 raises its profit). The second fact tells us that the firm's marginal revenue from selling its 21st unit must be less than its marginal cost of producing that unit (which is why selling unit #21 lowers its profit).

Note that MR > MC for unit 20, and MR < MC for unit 21 is all the information in the question tells us. We are told only that selling unit 20 increases the firm's profit, but we are not told by how much profit rises. We therefore do not know by how much MR exceeds MC. Correspondingly, knowing only that selling unit 21 decreases the firm's profit does not tell us by how much MC exceeds MR.

As was the case for the last question, you may get into trouble if you misunderstand the relationships between profit, total revenue and total cost, and marginal revenue and marginal cost. The question tells us that Firm XYZ earns a bigger profit when it sells 20 units than it would earn if it sold 19 units or 21 units. This is equivalent to saying that the difference between the firm's total revenue and its total cost when it sells 20 units is bigger than is the difference between its TR and TC when it sells 19 or 21. Knowing something about profit tells us something about the gap between TR and TC. In contrast, knowing how profit is changing tells us something about MR compares with MC.

Answer (a) states that knowing that profit is maximized at 20 units tells us that the marginal revenue of the 20th unit exceeds its marginal cost by more than MR exceeds MC for any other unit. This is incorrect. Here are the statements that are correct. First, when the firm sells 20 units, its total revenue exceeds its total cost by more than TR exceeds TC for 19 or 21 or any other number of units. Second, the marginal revenue of selling the 20th unit exceeds the marginal cost of producing it by some amount (but perhaps by a fairly small amount).

Question 3 answer is:   c.   5

Explanation: There's more than one way to answer this question, but the method I'd suggest involves comparing marginal revenue and marginal cost. Remember from class (and from the answers to earlier questions) that a firm maximizes its profit by selling every unit for which marginal revenue exceeds marginal cost (even if it MR exceeds MC by just a little bit).

In this question, marginal revenue is always $20. We know this because the problem tells us that Betty can sells as many units of the output as she wishes at $20 per unit, which means that every time Betty sells one more unit her total revenue rises by $20.

The table in the question gives Betty's total cost of producing the first five units of output. Since marginal cost is defined as the change in total cost that results from producing the last unit, it's easy to compute the marginal cost of producing each output. For example, when Betty increases her production from 1 unit to 2 units, her total cost rises from $37 to $45. Thus, the marginal cost of producing the second unit is $8.

The accompanying table gives the marginal cost of producing units 2 through 7. It also shows (as noted above) that the marginal revenue of every unit equals $20.

Quantity	Total Cost	Marginal Cost	Marginal Revenue
1	$37	--	$20
2	$45	$8	$20
3	$55	$10	$20
4	$68	$13	$20
5	$86	$18	$20
6	$111	$25	$20
7	$145	$34	$20

Given these numbers, it is clearly in Betty's interest to sell the the second unit, the third unit, the fourth units, and the fifth . Consider unit number five, for instance. Selling that unit causes Betty's revenue to rise by $20, and her cost to rise by $18. Since MR exceeds MC by $2, selling this unit raises Betty's profit. Note that selling the fifth unit doesn't increase Betty's profit by as much as did selling the fourth unit, but the fifth unit does raise her profit.

If Betty increased her sales from five units to six units, however, her revenue would rise by $20 while her cost rose by $25. Selling the sixth unit would thus decrease Betty's profit. [Note that Betty's profit would still be positive; it just wouldn't be as large as it could be.] In order to maximize her profit. therefore, Betty should thus sell five units, but no more.

Note: as a general rule in answering questions of this type, you should take whatever information is given, and convert that information into marginal revenue and marginal cost. MR and MC can be directly compared, but you'll always run into trouble if you try to compare marginal revenue with total cost (or total revenue with marginal cost).

Question 4 answer is:   a.   rise

Explanation: This is a question about whether a business should "open" or "close" in order to maximize its profit. The important point in this question is that the rent cost is not relevant to Frank's decision about whether or not to open on Sunday. Frank is committed to paying the same amount for rent regardless of his open-or-close-on-Sunday decision. His rent payment is thus independent of the decision on which we are focusing, and should therefore play no role in that decision.

In other words, from the point of view of the open-or-close-on-Sunday decision, all of Fred's rent payments are fixed and sunk.

The only costs that are directly related to Frank's Sunday decision are those that depend on that decision -- wages, electricity, and cost of the things that are sold. These are costs that Frank can avoid if he chooses to open the store. In other words, these are variable costs over which Frank has control (costs that depend on his decision).

If Frank's revenue from opening on Sunday exceeds his variable cost of so doing, then opening on Sundays will increase his profit. If Frank's revenue from opening on Sunday is less than his variable cost, then so doing will lower his profit.

In this question, if Frank opens the store on Sunday, he incurs $280 in variable cost (wages plus electricity plus his costs of the products sold) and collects $300 in revenue. Frank would therefore increase his profit by opening on Sunday. The "$40 daily rent" cost is irrelevant to this decision because Frank has to pay it regardless of whether he opens the store or not.

Question 5 answer is:   b.   is currently earning a (total) profit that is greater than $500

Explanation: One of the definitions of profit is that profit = ( price - average total cost ) × quantity. Plugging in the question's values for P, ATC, and Q produces profit = ( 10 - 8 ) × 300 = 600. The firm is thus currently earning a profit that exceeds $500.

When this firm produced its 300th unit, the price at which it sold its product was $10. The firm's marginal cost of producing that unit was also $10.

If the firm is a price taker (meaning that marginal revenue = price), then unit 300 is the unit for which P = MR = MC. In other words, the firm maximizes its profit by selling 300 units. Increasing production to 310 units therefore can't lead to greater profits (after all, profits were as big as they could be when 300 units were sold). Furthermore, the question tells us that for all units beyond #300, MC will exceed price, which means that selling those units would decrease the firm's profit.

[If the firm were a price setter (meaning that marginal revenue < price) -- which isn't really relevant for this question -- it is again true that increasing sales from 300 to 310 units can't increase profit, since marginal cost will exceed price which exceeds marginal revenue.]

This question emphasizes the difference between the condition that indicates a firm is currently earning a profit (which this firm is -- its selling price exceeds its average cost of production), and the condition that indicates whether or not the firm would increase its profit by increasing its sales (in this case, raising sales won't raise profit, because the firm's marginal cost of producing the additional units would exceed its marginal revenue from selling them).

Question 6 answer is:   c.   90

Explanation: As noted in class (and the textbook), one of the ways to measure profit is that profit = ( price - average total cost ) × quantity. Since that formula is of the form A × B, it is illustrated on a graph with a rectangle, the height of which measures the per-unit profit (P-ATC), and the width of which measures the quantity sold (Q), where both are measured at the quantity of output that allows the firm to earn its largest-possible profit.

In this problem, the firm mazimizes its profit by selling 30 units -- we know this because the firm's marginal cost curve hits the market price (which is also the marginal revenue of a price-taking firm) at Q = 30. At that quantity of output (Q = 30), the graph indicates that the firm's average total cost of production equals 13 -- it's three notches down from the market price of 16. Thus, the firm's profit -- as illustrated in the accompanying figure -- is (16-13) × 3 = 90 (a rectangle with height equal to 3 and width equal to 30).

The incorrect answers are based on the following calculations: (16-12) × 4 = 88 (but selling 12 units isn't a profit-maximizing decision); (16-12) × 4 = 120 (but when output is 30, ATC is 13 not 12); 16 × 22 = 352 and 16 × 30 = 480 (these are revenue calculations, not profit calculations.

Question 7 answer is:   d.   closer to  ;  a decrease

Explanation: When the sellers in a market are earning positive economic profits, it means that consumers value the good (i.e., they're willing to pay an amount to buy the good) that exceeds the (average) cost of producing it. In other words, the value of what is being produced exceeds the cost of the resources being used up to produce it. [This assumes none of the complications we'll discuss later in the semester.]

When the sellers in a market are earning positive economic profits, it also means that the "change" in the number of firms participating in the market will be a rise in the number of sellers.

The first paragraph implies that there would be a net benefit for society if more of the good was produced. The second paragraph tells us that entry will cause more of the good to be produced. Thus, the market outcome moves closer the economically-efficient outcome.

The entry of new firms causes an increase in market supply. The rightward movement of supply causes the market price to fall, which (other things unchanged) lowers the profits earned by the firms that were already in the market.

Question 8 answer is:   a.   flatter  ;  fall back towards the original price

Explanation: When the market price of a good rises, the quantity supplies rises. In the short run, the existing firms in the market can increase their output, but the extent to which each firm can do so is limited by the fact that the firm don't have enough time to change the quantity of the (at least one) input it has to use in a fixed amount. ["Short run" means that a firm doesn't have enough time to change its use of (at least) one fixed input.]

In the long run, firms can adjust their usage of all their inputs, and also the number of firms in the market can change. As a result, a given price change will create a larger change in quantity supplied in a market in the long run than in the short run. [For example, a price rise (as in this question) will cause existing firms to expand and new firms to enter the market.] The increased flexibility in the long run means that the long-run supply curve in a market will be flatter (or more elastic) than will the short-run supply curve.

An increase in demand will cause the market equilibrium to move up a supply curve. The after-demand-shift short-run equilibrium will be on the (steeper) short-run supply curve. The after-demand-shift long-run equilibrium will be on the (flatter) long-run supply curve. In other words, the short-run market equilibrium price will be higher than will the long-run equilibrium price. In response to the (permanent) increase in demand, the price first rises to (higher) short-run equilibrium level, and then drops somewhat back to its (lower) long-run equilibrium level.

Another way to describe the pattern of price movement is that the rise in demand causes the market equilibrium price to rise in the short run. This short-run rise in price leads the existing firms to expand their production and leads new firms to enter the market. As these changes occur, the short-run supply curve shifts to the right, which causes the price to fall back towards its original level. [Since the question says that the long-run supply curve is upward-sloping, we know that, while the expansion of production reverses some of the original price rise, the price doesn't fall all the way back to its original level.]

Question 9 answer is:   e.   fall somewhere in the range between $18.00 and $22.00

Explanation: One way to answer this question is to simply plug numbers into the formula for Marginal Revenue given in class. That formula shows that selling an additional unit affects the firm's revenue in two ways. First, the firm's gain in revenue equals the price at which it sells the new unit. In order to sell that unit, however, the firm had to reduce its selling price, which means that the firm collects less on all the sales it would have made anyway (without the price reduction).

When Tou's Company sells 41 units, it price (for all those units) is $29.75 (since increasing sales from 40 to 41 units requires a 25 cent reduction from a price of $30).

The marginal revenue formula illustrates these two effects. According to the formula, Tou's Marginal Revenue from selling a 41st unit is expressed as:

Note that the numbers on the right-hand side of the formula depend on the number on the left-hand side. For example, the MR from selling the 42nd unit would equal (P at which 42nd was sold) - (41) (drop in price needed to sell 42nd unit).

[While it's not relevant to this question, also note the following. If a firm can sell more units without having to decrease its price in order to do so, the "drop in price" term in the above formula is zero. The formula then tells us that Marginal Revenue equals Price. This is the case of a "price taker" firm that can sell as much as it wants without needing to lower its price in order to do so.]

Plugging in the numbers from the problem, we see that the MR from selling the 41st unit = $29.75 - (40 × $.25) = $29.75 - $10 = $19.75. [Remember the "order of operations" -- one has to do the multiplication before doing the subtraction.]

The alternate way to answer this question is to find Tou's Total Revenue when it sells 40 units (at a price of $30 each) and its TR when it sells 41 units (at a price of $29.75 each).

In this example, Total Revenue when 40 units are sold is TR = 40 × $30 = $1200, and TR when 41 units are sold is TR = 41 × $29.75 = $1219.75. Clearly, selling the 41st unit increases Tou's Total Revenue by $19.75; its Marginal Revenue from selling the 41st unit is therefore $19.75.