# 7.2 The structure of costs in the short run  (Page 5/23)

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Whatever the firm’s quantity of production, total revenue must exceed total costs if it is to earn a profit. As explored in the chapter Choice in a World of Scarcity , fixed costs are often sunk costs    that cannot be recouped. In thinking about what to do next, sunk costs should typically be ignored, since this spending has already been made and cannot be changed. However, variable costs can be changed, so they convey information about the firm’s ability to cut costs in the present and the extent to which costs will increase if production rises.

## Why are total cost and average cost not on the same graph?

Total cost, fixed cost, and variable cost each reflect different aspects of the cost of production over the entire quantity of output being produced. These costs are measured in dollars. In contrast, marginal cost, average cost, and average variable cost are costs per unit. In the previous example, they are measured as cost per haircut. Thus, it would not make sense to put all of these numbers on the same graph, since they are measured in different units ($versus$ per unit of output).

It would be as if the vertical axis measured two different things. In addition, as a practical matter, if they were on the same graph, the lines for marginal cost, average cost, and average variable cost would appear almost flat against the horizontal axis, compared to the values for total cost, fixed cost, and variable cost. Using the figures from the previous example, the total cost of producing 40 haircuts is $320. But the average cost is$320/40, or $8. If you graphed both total and average cost on the same axes, the average cost would hardly show. Average cost tells a firm whether it can earn profits given the current price in the market. If we divide profit by the quantity of output produced we get average profit , also known as the firm’s profit margin . Expanding the equation for profit gives: But note that: Thus: This is the firm’s profit margin . This definition implies that if the market price is above average cost, average profit, and thus total profit, will be positive; if price is below average cost, then profits will be negative. The marginal cost of producing an additional unit can be compared with the marginal revenue gained by selling that additional unit to reveal whether the additional unit is adding to total profit—or not. Thus, marginal cost helps producers understand how profits would be affected by increasing or decreasing production. ## A variety of cost patterns The pattern of costs varies among industries and even among firms in the same industry. Some businesses have high fixed costs, but low marginal costs. Consider, for example, an Internet company that provides medical advice to customers. Such a company might be paid by consumers directly, or perhaps hospitals or healthcare practices might subscribe on behalf of their patients. Setting up the website, collecting the information, writing the content, and buying or leasing the computer space to handle the web traffic are all fixed costs that must be undertaken before the site can work. However, when the website is up and running, it can provide a high quantity of service with relatively low variable costs, like the cost of monitoring the system and updating the information. In this case, the total cost curve might start at a high level, because of the high fixed costs, but then might appear close to flat, up to a large quantity of output, reflecting the low variable costs of operation. If the website is popular, however, a large rise in the number of visitors will overwhelm the website, and increasing output further could require a purchase of additional computer space. For other firms, fixed costs may be relatively low. For example, consider firms that rake leaves in the fall or shovel snow off sidewalks and driveways in the winter. For fixed costs, such firms may need little more than a car to transport workers to homes of customers and some rakes and shovels. Still other firms may find that diminishing marginal returns set in quite sharply. If a manufacturing plant tried to run 24 hours a day, seven days a week, little time remains for routine maintenance of the equipment, and marginal costs can increase dramatically as the firm struggles to repair and replace overworked equipment. Every firm can gain insight into its task of earning profits by dividing its total costs into fixed and variable costs, and then using these calculations as a basis for average total cost, average variable cost, and marginal cost. However, making a final decision about the profit-maximizing quantity to produce and the price to charge will require combining these perspectives on cost with an analysis of sales and revenue, which in turn requires looking at the market structure in which the firm finds itself. Before we turn to the analysis of market structure in other chapters, we will analyze the firm’s cost structure from a long-run perspective. ## Key concepts and summary In a short-run perspective, a firm’s total costs can be divided into fixed costs, which a firm must incur before producing any output, and variable costs, which the firm incurs in the act of producing. Fixed costs are sunk costs; that is, because they are in the past and cannot be altered, they should play no role in economic decisions about future production or pricing. Variable costs typically show diminishing marginal returns, so that the marginal cost of producing higher levels of output rises. Marginal cost is calculated by taking the change in total cost (or the change in variable cost, which will be the same thing) and dividing it by the change in output, for each possible change in output. Marginal costs are typically rising. A firm can compare marginal cost to the additional revenue it gains from selling another unit to find out whether its marginal unit is adding to profit. Average total cost is calculated by taking total cost and dividing by total output at each different level of output. Average costs are typically U-shaped on a graph. If a firm’s average cost of production is lower than the market price, a firm will be earning profits. Average variable cost is calculated by taking variable cost and dividing by the total output at each level of output. Average variable costs are typically U-shaped. If a firm’s average variable cost of production is lower than the market price, then the firm would be earning profits if fixed costs are left out of the picture. ## Problems Return to [link] . What is the marginal gain in output from increasing the number of barbers from 4 to 5 and from 5 to 6? Does it continue the pattern of diminishing marginal returns? Compute the average total cost, average variable cost, and marginal cost of producing 60 and 72 haircuts. Draw the graph of the three curves between 60 and 72 haircuts. #### Questions & Answers why do the people demand for money in the economy. Amandi Reply Because money helps in driving every activity in the economy. Akoto Also to meet the needs of all. Akoto Because it is the purchasing power Lawrence For speculative motive Emmanuel because it is portable Jorge Is only the purchasing power for exchanging of goods and services Addin is also better than trade and bater Jorge how to calculate national income Mujittapha how to calculate national income Mujittapha What do you means by patten law in economic? Tamba Reply Do you mean patent law or patten law? Addin Patent I'm sorry.. Tamba Australian patent law is law governing the granting of a temporary monopoly on the use of an invention, in exchange for the publication and free use of the invention after a certain time. The primary piece of legislation is thePatents Act 1990 (Cth). Addin law is important thing Anthony yeah is important Jorge Demand for canned goods when it was reported that super typhoon hagupit will landfall in the Philippine area of responsibility on sunday night leonard Reply opportunity cost ? abdullah opportunity cost is the alternative forgone after making a choice Kotey what is macroeconomic ALIYU Reply its the study of the interractions of the various components of economics as a whole Kotey please suggest me topic for research, about following issues 1. labor migration & economic growth 2. terrorism and trade 3. religious pessimism and trad Fayaz Reply state the law of diminishing returns. Ronaxic Reply the law diminishing returns states that as more and more units of variable factors of production(such as capital, labour) are combined with a fixed factor (such as land) after a certain point, the marginal product diminishes or declines Vanessa I would like to add one more point In the above statement. The addition of more variable factors of production will only leads to diminishing returns if the existing fixed capacity is fully utilised. Ankit what is diminishing marginal utility Ronaxic Reply with more units of consumption of a same commodity you will feel less satisfied with every next commodity. if you are thirsty you purchase a bottle of Coca-Cola and drink it, you will be satisfied at the same time again you drink another bottle of Cola you will be less satisfied in comparison. Ankit utility nothing it is just a measurement of your satisfaction. Ankit and diminishes as long as you consume same commodity continuously Ankit how to calculate the national income Mujittapha what is the problem of economic in the world? jacob i think the problem of economics is how to use scarce resources to satisfy unlimited wants Kotey what is taxation K.visor Reply levy paid by eligible individuals and companies to the government Kingt tax Raji A means by which governments finance their expenditure by imposing charges on citizens and corporate entities. Governments use taxation to encourage or discourage certain economic decisions. Raji a source of economic revenue in which working citizens pay levy which varies from one individual to the other. Vanessa monies paid by residents of a country to the government in which the residents benefit indirectly Kotey it's the government, looking for funding to create public goods and services so that everyone can be happy. Sinethemba why does the demand curve slop downward Ronaxic thanks Ronaxic why does the demand curve slop downward? Ronaxic the demand curve is nothing but a line which shows willingness to purchase a commodity or a thing.For example, if you want to purchase a Pepsi can you are willing to purchase 5 Pepsi cans if they are of$3 each. but if they are of \$5 each you want to purchase only three of them.
Ankit
so at Higher prices you like to purchase less quantity that's why demand curve falls down words. but please note demand curve does not fall downwards always for inferior goods the rise up parts like a supply curve because at Higher prices you tend to purchase those goods more
Ankit
and at lower prices of inferior goods you tend to avoid them and relocate your Limited money to other goods.
Ankit
what is taxation?
In simple term. Taxation can be defined as compulsory payment levy on company or individual by the government. It can be direct or indirect.
salawu
what is capital
K.visor
its nice
Belaisan
it's nice
Abdulwali
capital , it is a investment of money or assets which is invested before starting up of the business
its nice
Belaisan
it won't let you sleep
Ankit
Please any Ghanaian schooling at KNUST?
combining factors of production is the role of
the situation in economic where by a more valuable good is sold at a low price while less valuable good is sold at a higher price .how can we describe this situation in economic
Fung
price discrimination
Fayaz
deman and supply
Samim
price discrimination
Citizen
enterlrenure
Fayaz
you can take example of water and daimond. you can ask someone to choose anyone from above 1. to a person in a Sahara desert and 2. a girl in London. you will get your answer
Ankit
it depends upon the buyer's preference what he wants why he wants and what is the necessity of that product at current time.
Ankit
causes of high elasticity of demand
causes of high elasticity of supply
Onyango
what is optimazation
lepekola
lepekola
A trade-off  is a situational decision that involves diminishing one quality, or property of a design in return for gains in other aspects.
what is indifference curve ?
abdullah
its represnted by the loops of points and gives same level of satisfaction
hisham
what is enterpreneurship
Kukoyi
Entrepreneurship is the talent, knowledge and willingness individual has to engage in an activity that can result in new kind of firm
what is the short run industry supply curves?
james
I think there' s a mistake. P = - 0.4 + 0.2Qs is the supply curve and not the demand curve. Am I correct?
Qs is quantity supplied
The
This is what I think
The
this eaquation is supply curve Qs=P-0.4 the relationship is positive when the price increase the Qs increase....
mukhtaar
since Qs is quantity supplied P= -0.4 + 0.2Qs =>P +0.4=0.2Qs =>P/0.2 + 0.4=Qs I made Qs the subject of the formula or equation. So your answer is correct
The
P = -0.4 + 0.2Qs is the same as P/0.2+0.4=Qs Price has a direct relationship with the quantity supplied i.e the higher the price the higher the quantity supplied. that is why it is +0.4(this is the quantity and it is postive) and P/O.2(is the price and it is positive).
The
For the demand equation let me give an example 0.2P-0.4=Qd. Here the P is postive(+0.2) and the quantity which is -O.4 is negative( because of the negative sign(-) there is an inverse relationship between price and quantity. For quantity demanded the higher the price the lower the quantuty.
The
It's how I understand it
The
0.2P-0.4=Qd. the equation is wrong because the price have direct ralationship Quantity demanded but the correct equation is-0.2P -0.4=Qd so the higher price the lower Quantity
mukhtaar
I think the relationship is inverse because of the negative sign(-)
The
ok You mean the price and quantity demanded should be negative(inverse relationship) for Qd and the price and quantity supplied should be postive(direct relationship) for Qs
The
thank you for the correction
The
yes because it got a positive gradient of +0.2
Michael
This is the mistake I found: "Since P is on the vertical axis, it is easiest if you solve each equation for P. The demand curve is then P = 8 – 0.5Qd and the demand curve is P = –0.4 + 0.2Qs. Note that the vertical intercepts are 8 and –0.4, and the slopes are –0.5 for demand and 0.2 for supply."
Valeria
dear price do not depend on quantity. rather quantity depends on price. so the equation should be Qty=0.2Px-0.4
Michael
please can someone generate supply equation for me
ok
Detto
Qs=f(P,Pr,G,E,Z,Pf,)
The
where p is price, Pr is price of related goods, G is goals of a firm E is supplier's future expectation of prices,Z is other related factors, Pf is cost of factors of production.
The
I think it's wrong
The
if Qd=90-p Qs=90+p
The
the coefficient of price must be positive since supply curve is positively slopping
Kotey
yes
The
it's true. thank you
The
welcome
Kotey
ok
The
OK, thank you
David
no one can do that, you must determine the the key factors for the commodity, like price, income, prices of alternative commodity, and other factors, if you want the main equation, you must have 4 values, 2 values for each quantity and price, for one commodity
Chief